sqlite tutorial

sqlite3/README.md

@@ -1,4 +0,0 @@
-sqlite3_examples
-================
-
-Syntax examples for working with SQLite databases via the sqlite3 module in Python

sqlite3/create_db.py

@@ -1,30 +0,0 @@
-# 10/28/2013 Sebastian Raschka
-# Syntax basics for creating sqlite3 data bases
-
-import sqlite3
-
-# create new db and make connection
-conn = sqlite3.connect('zinc_db1.db')    
-c = conn.cursor()
-
-# create table
-c.execute('''CREATE TABLE zinc_db1
-             (zinc_id PRIMARY KEY, purchasable TEXT, non_rot_bonds INT)''')
-
-# Insert one row of data
-c.execute("INSERT INTO zinc_db1 VALUES ('ZINC00895032','YES', 4)")
-
-# Insert multiple lines of data
-multi_lines =[ ('ZINC00895033','YES', 1),
-	       ('ZINC00895034','NO', 0),
-	       ('ZINC00895035','YES', 3),
-	       ('ZINC00895036','YES', 9),
-	       ('ZINC00895037','YES', 10) 
-	      ]
-c.executemany('INSERT INTO zinc_db1 VALUES (?,?,?)', multi_lines)
-
-# Save (commit) the changes
-conn.commit()
-
-# close connection
-conn.close()

sqlite3/query_db.py

@@ -1,28 +0,0 @@
-# 10/28/2013 Sebastian Raschka
-# Syntax basics for querying sqlite3 data bases
-
-import sqlite3
-
-# open existing database
-conn = sqlite3.connect('zinc_db1.db')    
-c = conn.cursor()
-
-# print all lines ordered by number of non_rot_bonds
-for row in c.execute('SELECT * FROM zinc_db1 ORDER BY non_rot_bonds'):
-    print row
-
-# print all lines that are purchasable and have <= 7 rotatable bonds
-t = ('YES',7,)
-for row in c.execute('SELECT * FROM zinc_db1 WHERE purchasable=? AND non_rot_bonds <= ?', t):
-	print row
-
-# print all lines that are purchasable and have <= 7 rotatable bonds
-t = ('YES',7,)
-c.execute('SELECT * FROM zinc_db1 WHERE purchasable=? AND non_rot_bonds <= ?', t)
-rows = c.fetchall()
-for r in rows:
-    print r
-
-# close connection
-conn.close()
-

sqlite3/update_db.py

@@ -1,46 +0,0 @@
-# 10/28/2013 Sebastian Raschka
-# Syntax basics for updating sqlite3 data bases
-
-import sqlite3
-
-# make connection to existing db
-conn = sqlite3.connect('zinc_db1.db')
-c = conn.cursor()
-
-# update field (no insert if id doesn't exist)
-t = ('NO', 'ZINC00895033', )
-c.execute("UPDATE zinc_db1 SET purchasable=? WHERE zinc_id=?", t)
-print "Total number of rows changed:", conn.total_changes
-
-
-# update, or insert when id does not exist
-# here: updates rotatable bonds if record with primary key zinc_id exists,<br>  
-#     else inserts new record an sets purchasable to 0
-c.execute("""INSERT OR REPLACE INTO zinc_db1 (zinc_id, rotatable_bonds, purchasable)
-              VALUES ( 'ZINC123456798', 
-                3, 
-                COALESCE((SELECT purchasable from zinc_db1 WHERE zinc_id = 'ZINC123456798'), 0)
-              )""")
-
-
-
-# delete rows
-t = ('NO', )
-c.execute("DELETE FROM zinc_db1 WHERE purchasable=?", t)
-print "Total number of rows deleted: ", conn.total_changes
-
-# add column
-c.execute("ALTER TABLE zinc_db1 ADD COLUMN 'keto_oxy' TEXT")
-
-# save changes
-conn.commit()
-
-# print column names
-c.execute("SELECT * FROM zinc_db1")
-col_name_list = [tup[0] for tup in c.description]
-print col_name_list
-
-
-
-# close connection
-conn.close()

sqlite3_howto/LICENSE

@@ -0,0 +1,674 @@
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+<http://www.gnu.org/philosophy/why-not-lgpl.html>.

sqlite3_howto/README.md

@@ -0,0 +1,784 @@
+## A thorough guide to SQLite database operations in Python
+
+_\-- written by Sebastian Raschka_ on March 7, 2014
+
+
+  
+  
+
+![sqlite_python_logo.png](../Images/sqlite_python_logo.png)
+
+  
+  
+
+* * *
+
+#### Sections
+
+• Connecting to an SQLite database  
+• Creating a new SQLite database  
+      - Overview of SQLite data types  
+      - A quick word on PRIMARY KEYS:  
+• Adding new columns  
+• Inserting and updating rows  
+• Creating unique indexes  
+• Querying the database - Selecting rows  
+• Security and injection attacks  
+• Date and time operations  
+• Printing a database summary  
+• Conclusion  
+
+The complete Python code that I am using in this tutorial can be downloaded
+from my GitHub repository: <https://github.com/rasbt/python_sqlite_code>  
+  
+
+* * *
+
+  
+
+## Connecting to an SQLite database
+
+The sqlite3 that we will be using throughout this tutorial is part of the
+Python Standard Library and is a nice and easy interface to SQLite databases:
+There are no server processes involved, no configurations required, and no
+other obstacles we have to worry about.
+
+In general, the only thing that needs to be done before we can perform any
+operation on a SQLite database via Python's `sqlite3` module, is to open a
+connection to an SQLite database file:
+
+    
+    
+    import sqlite3
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    
+
+where the database file (`sqlite_file`) can reside anywhere on our disk, e.g.,
+
+    
+    
+    sqlite_file = '/Users/Sebastian/Desktop/my_db.sqlite' 
+    
+
+Conveniently, a new database file (`.sqlite` file) will be created
+automatically the first time we try to connect to a database. However, we have
+to be aware that it won't have a table, yet. In the following section, we will
+take a look at some example code of how to create a new SQLite database files
+with tables for storing some data.
+
+To round up this section about connecting to a SQLite database file, there are
+two more operations that are worth mentioning. If we are finished with our
+operations on the database file, we have to close the connection via the
+`.close()` method:
+
+    
+    
+    conn.close()
+    
+
+And if we performed any operation on the database other than sending queries,
+we need to commit those changes via the `.commit()` method before we close the
+connection:
+
+    
+    
+    conn.commit()
+    conn.close()
+    
+
+  
+
+## Creating a new SQLite database
+
+Let us have a look at some example code to create a new SQLite database file
+with two tables: One with and one without a PRIMARY KEY column (don't worry,
+there is more information about PRIMARY KEYs further down in this section).
+
+    
+    
+    mport sqlite3
+    
+    sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+    table_name1 = 'my_table_1'  # name of the table to be created
+    table_name2 = 'my_table_2'  # name of the table to be created
+    new_field = 'my_1st_column' # name of the column
+    field_type = 'INTEGER'  # column data type
+    
+    # Connecting to the database file
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    
+    # Creating a new SQLite table with 1 column
+    c.execute('CREATE TABLE {tn} ({nf} {ft})'\
+            .format(tn=table_name1, nf=new_field, ft=field_type))
+    
+    # Creating a second table with 1 column and set it as PRIMARY KEY
+    # note that PRIMARY KEY column must consist of unique values!
+    c.execute('CREATE TABLE {tn} ({nf} {ft} PRIMARY KEY)'\
+            .format(tn=table_name2, nf=new_field, ft=field_type))
+    
+    # Committing changes and closing the connection to the database file
+    conn.commit()
+    conn.close()
+    
+
+Download the script: [create_new_db.py](https://raw.github.com/rasbt/python_sq
+lite_code/master/code/create_new_db.py)
+
+* * *
+
+**Tip:** A handy tool to visualize and access SQLite databases is the free FireFox [SQLite Manager](https://addons.mozilla.org/en-US/firefox/addon/sqlite-manager/?src) add-on. Throughout this article, I will use this tool to provide screenshots of the database structures that we created below the corresponding code sections.
+
+* * *
+
+  
+  
+
+![1_sqlite3_init_db.png](../Images/1_sqlite3_init_db.png)  
+  
+Using the code above, we created a new `.sqlite` database file with 2 tables.
+Each table consists of currently one column only, which is of type INTEGER.
+
+  
+
+* * *
+
+**Here is a quick overview of all data types that are supported by SQLite 3:**
+
+  * INTEGER: A signed integer up to 8 bytes depending on the magnitude of the value.
+  * REAL: An 8-byte floating point value.
+  * TEXT: A text string, typically UTF-8 encoded (depending on the database encoding).
+  * BLOB: A blob of data (binary large object) for storing binary data.
+  * NULL: A NULL value, represents missing data or an empty cell.
+
+* * *
+
+Looking at the table above, You might have noticed that SQLite 3 has no
+designated Boolean data type. However, this should not be an issue, since we
+could simply re-purpose the INTEGER type to represent Boolean values (0 =
+false, 1 = true).
+
+  
+
+**A quick word on PRIMARY KEYS:**  
+In our example code above, we set our 1 column in the second table to PRIMARY
+KEY. The advantage of a PRIMARY KEY index is a significant performance gain if
+we use the PRIMARY KEY column as query for accessing rows in the table. Every
+table can only have max. 1 PRIMARY KEY (single or multiple column(s)), and the
+values in this column MUST be unique! But more on column indexing in the a
+later section.
+
+  
+
+## Adding new columns
+
+If we want to add a new column to an existing SQLite database table, we can
+either leave the cells for each row empty (NULL value), or we can set a
+default value for each cell, which is pretty convenient for certain
+applications.  
+Let's have a look at some code:
+
+    
+    
+    import sqlite3
+    
+    sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+    table_name = 'my_table_2'   # name of the table to be created
+    id_column = 'my_1st_column' # name of the PRIMARY KEY column
+    new_column1 = 'my_2nd_column'  # name of the new column
+    new_column2 = 'my_3nd_column'  # name of the new column
+    column_type = 'TEXT' # E.g., INTEGER, TEXT, NULL, REAL, BLOB
+    default_val = 'Hello World' # a default value for the new column rows
+    
+    # Connecting to the database file
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    
+    # A) Adding a new column without a row value
+    c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}' {ct}"\
+            .format(tn=table_name, cn=new_column1, ct=column_type))
+    
+    # B) Adding a new column with a default row value
+    c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}' {ct} DEFAULT '{df}'"\
+            .format(tn=table_name, cn=new_column2, ct=column_type, df=default_val))
+    
+    # Committing changes and closing the connection to the database file
+    conn.commit()
+    conn.close()
+    
+
+Download the script: [add_new_column.py](https://raw.github.com/rasbt/python_s
+qlite_code/master/code/add_new_column.py)
+
+  
+  
+![2_sqlite3_add_col.png](../Images/2_sqlite3_add_col.png)  
+  
+
+We just added 2 more columns (`my_2nd_column` and `my_3rd_column`) to
+`my_table_2` of our SQLite database next to the PRIMARY KEY column
+`my_1st_column`.  
+The difference between the two new columns is that we initialized
+`my_3rd_column` with a default value (here:'Hello World'), which will be
+inserted for every existing cell under this column and for every new row that
+we are going to add to the table if we don't insert or update it with a
+different value.
+
+  
+
+## Inserting and updating rows
+
+Inserting and updating rows into an existing SQLite database table - next to
+sending queries - is probably the most common database operation. The
+Structured Query Language has a convenient `UPSERT` function, which is
+basically just a merge between UPDATE and INSERT: It inserts new rows into a
+database table with a value for the PRIMARY KEY column if it does not exist
+yet, or updates a row for an existing PRIMARY KEY value. Unfortunately, this
+convenient syntax is not supported by the more compact SQLite database
+implementation that we are using here. However, there are some workarounds.
+But let us first have a look at the example code:
+
+    
+    
+    import sqlite3
+    
+    sqlite_file = 'my_first_db.sqlite'
+    table_name = 'my_table_2'
+    id_column = 'my_1st_column'
+    column_name = 'my_2nd_column'
+    
+    # Connecting to the database file
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    
+    # A) Inserts an ID with a specific value in a second column 
+    try:
+        c.execute("INSERT INTO {tn} ({idf}, {cn}) VALUES (123456, 'test')".\
+            format(tn=table_name, idf=id_column, cn=column_name))
+    except sqlite3.IntegrityError:
+        print('ERROR: ID already exists in PRIMARY KEY column {}'.format(id_column))
+    
+    # B) Tries to insert an ID (if it does not exist yet)
+    # with a specific value in a second column 
+    c.execute("INSERT OR IGNORE INTO {tn} ({idf}, {cn}) VALUES (123456, 'test')".\
+            format(tn=table_name, idf=id_column, cn=column_name))
+    
+    # C) Updates the newly inserted or pre-existing entry            
+    c.execute("UPDATE {tn} SET {cn}=('Hi World') WHERE {idf}=(123456)".\
+            format(tn=table_name, cn=column_name, idf=id_column))
+    
+    conn.commit()
+    conn.close()
+    
+
+Download the script: [update_or_insert_records.py](https://raw.github.com/rasb
+t/python_sqlite_code/master/code/update_or_insert_records.py)  
+  
+![3_sqlite3_insert_update.png](../Images/3_sqlite3_insert_update.png)  
+  
+Both A) `INSERT` and B) `INSERT OR IGNORE` have in common that they append new
+rows to the database if a given PRIMARY KEY does not exist in the database
+table, yet. However, if we'd try to append a PRIMARY KEY value that is not
+unique, a simple `INSERT` would raise an `sqlite3.IntegrityError` exception,
+which can be either captured via a try-except statement (case A) or
+circumvented by the SQLite call `INSERT OR IGNORE` (case B). This can be
+pretty useful if we want to construct an `UPSERT` equivalent in SQLite. E.g.,
+if we want to add a dataset to an existing database table that contains a mix
+between existing and new IDs for our PRIMARY KEY column.
+
+  
+
+## Creating unique indexes
+
+Just like hashtable-datastructures, indexes function as direct pointers to our
+data in a table for a particular column (i.e., the indexed column). For
+example, the PRIMARY KEY column would have such an index by default. The
+downside of indexes is that every row value in the column must be unique.
+However, it is recommended and pretty useful to index certain columns if
+possible, since it rewards us with a significant performance gain for the data
+retrieval.  
+The example code below shows how to add such an unique index to an existing
+column in an SQLite database table. And if we should decide to insert non-
+unique values into a indexed column later, there is also a convenient way to
+drop the index, which is also shown in the code below.
+
+    
+    
+    import sqlite3
+    
+    sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+    table_name = 'my_table_2'   # name of the table to be created
+    id_column = 'my_1st_column' # name of the PRIMARY KEY column
+    new_column = 'unique_names'  # name of the new column
+    column_type = 'TEXT' # E.g., INTEGER, TEXT, NULL, REAL, BLOB
+    index_name = 'my_unique_index'  # name for the new unique index
+    
+    # Connecting to the database file
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    
+    # Adding a new column and update some record
+    c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}' {ct}"\
+            .format(tn=table_name, cn=new_column, ct=column_type))
+    c.execute("UPDATE {tn} SET {cn}='sebastian_r' WHERE {idf}=123456".\
+            format(tn=table_name, idf=id_column, cn=new_column))
+    
+    # Creating an unique index
+    c.execute('CREATE INDEX {ix} on {tn}({cn})'\
+            .format(ix=index_name, tn=table_name, cn=new_column))
+    
+    # Dropping the unique index
+    # E.g., to avoid future conflicts with update/insert functions
+    c.execute('DROP INDEX {ix}'.format(ix=index_name))
+    
+    # Committing changes and closing the connection to the database file
+    conn.commit()
+    conn.close()
+    
+
+Download the script: [create_unique_index.py](https://raw.github.com/rasbt/pyt
+hon_sqlite_code/master/code/create_unique_index.py)  
+  
+![4_sqlite3_unique_index.png](../Images/4_sqlite3_unique_index.png)  
+  
+
+  
+
+## Querying the database - Selecting rows
+
+After we learned about how to create and modify SQLite databases, it's about
+time for some data retrieval. The code below illustrates how we can retrieve
+row entries for all or some columns if they match certain criteria.
+
+    
+    
+    import sqlite3
+    
+    sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+    table_name = 'my_table_2'   # name of the table to be queried
+    id_column = 'my_1st_column'
+    some_id = 123456
+    column_2 = 'my_2nd_column'
+    column_3 = 'my_3rd_column'    
+    
+    # Connecting to the database file
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    
+    # 1) Contents of all columns for row that match a certain value in 1 column
+    c.execute('SELECT * FROM {tn} WHERE {cn}="Hi World"'.\
+            format(tn=table_name, cn=column_2))
+    all_rows = c.fetchall()
+    print('1):', all_rows)
+    
+    # 2) Value of a particular column for rows that match a certain value in column_1 
+    c.execute('SELECT ({coi}) FROM {tn} WHERE {cn}="Hi World"'.\
+            format(coi=column_2, tn=table_name, cn=column_2))
+    all_rows = c.fetchall()
+    print('2):', all_rows)
+    
+    # 3) Value of 2 particular columns for rows that match a certain value in 1 column
+    c.execute('SELECT {coi1},{coi2} FROM {tn} WHERE {coi1}="Hi World"'.\
+            format(coi1=column_2, coi2=column_3, tn=table_name, cn=column_2))
+    all_rows = c.fetchall()
+    print('3):', all_rows)
+    
+    # 4) Selecting only up to 10 rows that match a certain value in 1 column
+    c.execute('SELECT * FROM {tn} WHERE {cn}="Hi World" LIMIT 10'.\
+            format(tn=table_name, cn=column_2))
+    ten_rows = c.fetchall()
+    print('4):', ten_rows)
+    
+    # 5) Check if a certain ID exists and print its column contents
+    c.execute("SELECT * FROM {tn} WHERE {idf}={my_id}".\
+            format(tn=table_name, cn=column_2, idf=id_column, my_id=some_id))
+    id_exists = c.fetchone()
+    if id_exists:
+        print('5): {}'.format(id_exists))
+    else:
+        print('5): {} does not exist'.format(some_id))
+    
+    # Closing the connection to the database file
+    conn.close()
+    
+
+Download the script: [selecting_entries.py](https://raw.github.com/rasbt/pytho
+n_sqlite_code/master/code/selecting_entries.py)  
+  
+
+![4_sqlite3_unique_index.png](../Images/4_sqlite3_unique_index.png)  
+  
+if we use the `.fetchall()` method, we return a list of tuples from the
+database query, where each tuple represents one row entry. The print output
+for the 5 different cases shown in the code above would look like this (note
+that we only have a table with 1 row here):  
+  
+![6_sqlite3_print_selecting_rows.png](../Images/6_sqlite3_print_selecting_rows
+.png)  
+  
+
+  
+
+## Security and injection attacks
+
+So far, we have been using Python's string formatting method to insert
+parameters like table and column names into the `c.execute()` functions. This
+is fine if we just want to use the database for ourselves. However, this
+leaves our database vulnerable to injection attacks. For example, if our
+database would be part of a web application, it would allow hackers to
+directly communicate with the database in order to bypass login and password
+verification and steal data.  
+In order to prevent this, it is recommended to use `?` place holders in the
+SQLite commands instead of the `%` formatting expression or the `.format()`
+method, which we have been using in this tutorial.  
+For example, instead of using
+
+    
+    
+    # 5) Check if a certain ID exists and print its column contents
+    c.execute("SELECT * FROM {tn} WHERE {idf}={my_id}".\
+            format(tn=table_name, cn=column_2, idf=id_column, my_id=some_id))
+    
+
+in the Querying the database - Selecting rows section above, we would want to
+use the `?` placeholder for the queried column value and include the
+variable(s) (here: `123456`), which we want to insert, as tuple at the end of
+the `c.execute()` string.
+
+    
+    
+    # 5) Check if a certain ID exists and print its column contents
+    c.execute("SELECT * FROM {tn} WHERE {idf}=?".\
+            format(tn=table_name, cn=column_2, idf=id_column), (123456,))   
+    
+
+However, the problem with this approach is that it would only work for values,
+not for column or table names. So what are we supposed to do with the rest of
+the string if we want to protect ourselves from injection attacks? The easy
+solution would be to refrain from using variables in SQLite queries whenever
+possible, and if it cannot be avoided, we would want to use a function that
+strips all non-alphanumerical characters from the stored content of the
+variable, e.g.,
+
+    
+    
+    def clean_name(some_var):
+        return ''.join(char for char in some_var if char.isalnum())
+    
+
+  
+
+## Date and time operations
+
+SQLite inherited the convenient date and time operations from SQL, which are
+one of my favorite features of the Structured Query Language: It does not only
+allow us to insert dates and times in various different formats, but we can
+also perform simple `+` and `-` arithmetic, for example to look up entries
+that have been added xxx days ago.
+
+    
+    
+    import sqlite3
+    
+    sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+    table_name = 'my_table_3'   # name of the table to be created
+    id_field = 'id' # name of the ID column
+    date_col = 'date' # name of the date column
+    time_col = 'time'# name of the time column
+    date_time_col = 'date_time' # name of the date & time column
+    field_type = 'TEXT'  # column data type
+    
+    # Connecting to the database file
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    
+    # Creating a new SQLite table with 1 column
+    c.execute('CREATE TABLE {tn} ({fn} {ft} PRIMARY KEY)'\
+            .format(tn=table_name, fn=id_field, ft=field_type))
+    
+    # A) Adding a new column to save date insert a row with the current date 
+    # in the following format: YYYY-MM-DD
+    # e.g., 2014-03-06
+    c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}'"\
+             .format(tn=table_name, cn=date_col))
+    # insert a new row with the current date and time, e.g., 2014-03-06
+    c.execute("INSERT INTO {tn} ({idf}, {cn}) VALUES('some_id1', DATE('now'))"\
+             .format(tn=table_name, idf=id_field, cn=date_col))
+    
+    # B) Adding a new column to save date and time and update with the current time
+    # in the following format: HH:MM:SS
+    # e.g., 16:26:37
+    c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}'"\
+             .format(tn=table_name, cn=time_col))
+    # update row for the new current date and time column, e.g., 2014-03-06 16:26:37
+    c.execute("UPDATE {tn} SET {cn}=TIME('now') WHERE {idf}='some_id1'"\
+             .format(tn=table_name, idf=id_field, cn=time_col))
+    
+    # C) Adding a new column to save date and time and update with current date-time
+    # in the following format: YYYY-MM-DD HH:MM:SS
+    # e.g., 2014-03-06 16:26:37
+    c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}'"\
+             .format(tn=table_name, cn=date_time_col))
+    # update row for the new current date and time column, e.g., 2014-03-06 16:26:37
+    c.execute("UPDATE {tn} SET {cn}=(CURRENT_TIMESTAMP) WHERE {idf}='some_id1'"\
+             .format(tn=table_name, idf=id_field, cn=date_time_col))
+    
+    # The database should now look like this:
+    # id         date           time        date_time
+    # "some_id1" "2014-03-06"   "16:42:30"  "2014-03-06 16:42:30"
+    
+    # 4) Retrieve all IDs of entries between 2 date_times
+    c.execute("SELECT {idf} FROM {tn} WHERE {cn} BETWEEN '2013-03-06 10:10:10' AND '2015-03-06 10:10:10'".\
+        format(idf=id_field, tn=table_name, cn=date_time_col))
+    all_date_times = c.fetchall()
+    print('4) all entries between ~2013 - 2015:', all_date_times)
+    
+    # 5) Retrieve all IDs of entries between that are older than 1 day and 12 hrs
+    c.execute("SELECT {idf} FROM {tn} WHERE DATE('now') - {dc} >= 1 AND DATE('now') - {tc} >= 12".\
+        format(idf=id_field, tn=table_name, dc=date_col, tc=time_col))
+    all_1day12hrs_entries = c.fetchall()
+    print('5) entries older than 1 day:', all_1day12hrs_entries)
+    
+    # Committing changes and closing the connection to the database file
+    conn.commit()
+    conn.close()
+    
+
+Download the script: [date_time_ops.py](https://raw.github.com/rasbt/python_sq
+lite_code/master/code/date_time_ops.py)
+
+  
+  
+![5_sqlite3_date_time.png](../Images/5_sqlite3_date_time.png)  
+  
+
+Some of the really convenient functions that return the current time and date
+are:
+
+* * *
+    
+    
+    DATE('now') # returns current date, e.g., 2014-03-06
+    TIME('now') # returns current time, e.g., 10:10:10
+    CURRENT_TIMESTAMP # returns current date and time, e.g., 2014-03-06 16:42:30
+    #  (or alternatively: DATETIME('now'))
+    
+
+* * *
+
+The screenshot below shows the print outputs of the code that we used to query
+for entries that lie between a specified date interval using
+
+    
+    
+    BETWEEN '2013-03-06 10:10:10' AND '2015-03-06 10:10:10'
+    
+
+and entries that are older than 1 day via
+
+    
+    
+    WHERE DATE('now') - some_date
+    
+
+Note that we don't have to provide the complete time stamps here, the same
+syntax applies to simple dates or simple times only, too.  
+  
+![5_sqlite3_date_time_2.png](../Images/5_sqlite3_date_time_2.png)  
+  
+
+  
+
+#### Update Mar 16, 2014:
+
+  
+If'd we are interested to calulate the hours between two `DATETIME()`
+timestamps, we can could use the handy `STRFTIME()` function like this  
+  
+
+    
+    
+    SELECT (STRFTIME('%s','2014-03-14 14:51:00') - STRFTIME('%s','2014-03-16 14:51:00'))  
+     / -3600
+    
+
+  
+which would calculate the difference in hours between two dates in this
+particular example above (here: `48`) in this case.  
+And to calculate the difference in hours between the current `DATETIME` and a
+given `DATETIME` string, we could use the following SQLite syntax:  
+  
+
+    
+    
+    SELECT (STRFTIME('%s',DATETIME('now')) - STRFTIME('%s','2014-03-15 14:51:00')) / 3600
+    
+
+  
+
+## Retrieving column names
+
+In the previous two sections we have seen how we query SQLite databases for
+data contents. Now let us have a look at how we retrieve its metadata (here:
+column names):
+
+    
+    
+    import sqlite3
+    
+    sqlite_file = 'my_first_db.sqlite'
+    table_name = 'my_table_3'
+    
+    # Connecting to the database file
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    
+    # Retrieve column information
+    # Every column will be represented by a tuple with the following attributes:
+    # (id, name, type, notnull, default_value, primary_key)
+    c.execute('PRAGMA TABLE_INFO({})'.format(table_name))
+    
+    # collect names in a list
+    names = [tup[1] for tup in c.fetchall()]
+    print(names)
+    # e.g., ['id', 'date', 'time', 'date_time']
+    
+    # Closing the connection to the database file
+    conn.close()
+    
+
+Download the script: [get_columnnames.py](https://raw.github.com/rasbt/python_
+sqlite_code/master/code/get_columnnames.py)  
+  
+![7_sqlite3_get_colnames_1.png](../Images/7_sqlite3_get_colnames_1.png)  
+  
+Since we haven't created a PRIMARY KEY column for `my_table_3`, SQLite
+automatically provides an indexed `rowid` column with unique ascending integer
+values, which will be ignored in our case. Using the `PRAGMA TABLE_INFO()`
+function on our table, we return a list of tuples, where each tuple contains
+the following information about every column in the table: `(id, name, type,
+notnull, default_value, primary_key)`.  
+So, in order to get the names of every column in our table, we only have to
+grab the 2nd value in each tuple of the returned list, which can be done by
+
+    
+    
+    names = [tup[1] for tup in c.fetchall()]
+
+after the `PRAGMA TABLE_INFO()` call. If we would print the contents of the
+variable `names` now, the output would look like this:  
+  
+![7_sqlite3_get_colnames_2.png](../Images/7_sqlite3_get_colnames_2.png)  
+  
+
+  
+
+## Printing a database summary
+
+I hope we covered most of the basics about SQLite database operations in the
+previous sections, and by now we should be well equipped to get some serious
+work done using SQLite in Python.  
+Let me conclude this tutorial with an obligatory "last but not least" and a
+convenient script to print a nice overview of SQLite database tables:
+
+    
+    
+    import sqlite3
+    
+    def connect(sqlite_file):
+        """ Make connection to an SQLite database file """
+        conn = sqlite3.connect(sqlite_file)
+        c = conn.cursor()
+        return conn, c
+    
+    def close(conn):
+        """ Commit changes and close connection to the database """
+        # conn.commit()
+        conn.close()
+    
+    def total_rows(cursor, table_name, print_out=False):
+        """ Returns the total number of rows in the database """
+        c.execute('SELECT COUNT(*) FROM {}'.format(table_name))
+        count = c.fetchall()
+        if print_out:
+            print('\nTotal rows: {}'.format(count[0][0]))
+        return count[0][0]
+    
+    def table_col_info(cursor, table_name, print_out=False):
+        """ 
+           Returns a list of tuples with column informations:
+          (id, name, type, notnull, default_value, primary_key)
+        
+        """
+        c.execute('PRAGMA TABLE_INFO({})'.format(table_name))
+        info = c.fetchall()
+        
+        if print_out:
+            print("\nColumn Info:\nID, Name, Type, NotNull, DefaultVal, PrimaryKey")
+            for col in info:
+                print(col)
+        return info
+    
+    def values_in_col(cursor, table_name, print_out=True):
+        """ Returns a dictionary with columns as keys and the number of not-null 
+            entries as associated values.
+        """
+        c.execute('PRAGMA TABLE_INFO({})'.format(table_name))
+        info = c.fetchall()
+        col_dict = dict()
+        for col in info:
+            col_dict[col[1]] = 0
+        for col in col_dict:
+            c.execute('SELECT ({0}) FROM {1} WHERE {0} IS NOT NULL'.format(col, table_name))
+            # In my case this approach resulted in a better performance than using COUNT
+            number_rows = len(c.fetchall())
+            col_dict[col] = number_rows
+        if print_out:
+            print("\nNumber of entries per column:")
+            for i in col_dict.items():
+                print('{}: {}'.format(i[0], i[1]))
+        return col_dict
+    
+    
+    if __name__ == '__main__':
+    
+        sqlite_file = 'my_first_db.sqlite'
+        table_name = 'my_table_3'
+    
+        conn, c = connect(sqlite_file)
+        total_rows(c, table_name, print_out=True)
+        table_col_info(c, table_name, print_out=True)
+        values_in_col(c, table_name, print_out=True) # slow on large data bases
+        
+        close(conn)
+    
+
+Download the script: [print_db_info.py](https://raw.github.com/rasbt/python_sq
+lite_code/master/code/print_db_info.py)  
+  
+![8_sqlite3_print_db_info_1.png](../Images/8_sqlite3_print_db_info_1.png)  
+  
+![8_sqlite3_print_db_info_2.png](../Images/8_sqlite3_print_db_info_2.png)
+
+  
+
+## Conclusion
+
+I really hope this tutorial was helpful to you to get started with SQLite
+database operations via Python. I have been using the `sqlite3` module a lot
+recently, and it has found its way into most of my programs for larger data
+analyses.  
+Currently, I am working on a novel drug screening software that requires me to
+store 3D structures and other functional data for ~13 million chemical
+compounds, and SQLite has been an invaluable part of my program to quickly
+store, query, analyze, and share my data.  
+Another smaller project that uses `sqlite3` in Python would be smilite, a
+module to retrieve and compare SMILE strings of chemical compounds from the
+free ZINC online database. If you are interested, you can check it out at:
+<https://github.com/rasbt/smilite>.  
+  
+If you have any suggestions or questions, please don't hesitate to write me an
+[ email](mailto:se.raschka@gmail.com) or leave a comment in the comment
+section below! I am looking forward to your opinions and ideas, and I hope I
+can improve and extend this tutorial in future.

sqlite3_howto/code/add_new_column.py

@@ -0,0 +1,28 @@
+# Sebastian Raschka, 2014
+# Adding a new column to an existing SQLite database
+
+import sqlite3
+
+sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+table_name = 'my_table_2'	# name of the table to be created
+id_column = 'my_1st_column' # name of the PRIMARY KEY column
+new_column1 = 'my_2nd_column'  # name of the new column
+new_column2 = 'my_3rd_column'  # name of the new column
+column_type = 'TEXT' # E.g., INTEGER, TEXT, NULL, REAL, BLOB
+default_val = 'Hello World' # a default value for the new column rows
+
+# Connecting to the database file
+conn = sqlite3.connect(sqlite_file)
+c = conn.cursor()
+
+# A) Adding a new column without a row value
+c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}' {ct}"\
+        .format(tn=table_name, cn=new_column1, ct=column_type))
+
+# B) Adding a new column with a default row value
+c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}' {ct} DEFAULT '{df}'"\
+        .format(tn=table_name, cn=new_column2, ct=column_type, df=default_val))
+
+# Committing changes and closing the connection to the database file
+conn.commit()
+conn.close()

sqlite3_howto/code/create_new_db.py

@@ -0,0 +1,27 @@
+# Sebastian Raschka, 2014
+# Creating a new SQLite database
+
+import sqlite3
+
+sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+table_name1 = 'my_table_1'	# name of the table to be created
+table_name2 = 'my_table_2'	# name of the table to be created
+new_field = 'my_1st_column' # name of the column
+field_type = 'INTEGER'  # column data type
+
+# Connecting to the database file
+conn = sqlite3.connect(sqlite_file)
+c = conn.cursor()
+
+# Creating a new SQLite table with 1 column
+c.execute('CREATE TABLE {tn} ({nf} {ft})'\
+        .format(tn=table_name1, nf=new_field, ft=field_type))
+
+# Creating a second table with 1 column and set it as PRIMARY KEY
+# note that PRIMARY KEY column must consist of unique values!
+c.execute('CREATE TABLE {tn} ({nf} {ft} PRIMARY KEY)'\
+        .format(tn=table_name2, nf=new_field, ft=field_type))
+
+# Committing changes and closing the connection to the database file
+conn.commit()
+conn.close()

sqlite3_howto/code/create_unique_index.py

@@ -0,0 +1,34 @@
+# Sebastian Raschka, 2014
+# Creating an index on a column with unique! values
+# Boosts performance for data base operations.
+
+import sqlite3
+
+sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+table_name = 'my_table_2'	# name of the table to be created
+id_column = 'my_1st_column' # name of the PRIMARY KEY column
+new_column = 'unique_names'  # name of the new column
+column_type = 'TEXT' # E.g., INTEGER, TEXT, NULL, REAL, BLOB
+index_name = 'my_unique_index'  # name for the new unique index
+
+# Connecting to the database file
+conn = sqlite3.connect(sqlite_file)
+c = conn.cursor()
+
+# Adding a new column and update some record
+c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}' {ct}"\
+        .format(tn=table_name, cn=new_column, ct=column_type))
+c.execute("UPDATE {tn} SET {cn}='sebastian_r' WHERE {idf}=123456".\
+        format(tn=table_name, idf=id_column, cn=new_column))
+
+# Creating an unique index
+c.execute('CREATE INDEX {ix} on {tn}({cn})'\
+        .format(ix=index_name, tn=table_name, cn=new_column))
+
+# Dropping the unique index
+# E.g., to avoid future conflicts with update/insert functions
+c.execute('DROP INDEX {ix}'.format(ix=index_name))
+
+# Committing changes and closing the connection to the database file
+conn.commit()
+conn.close()

sqlite3_howto/code/date_time_ops.py

@@ -0,0 +1,69 @@
+# Sebastian Raschka, 03/2014
+# Date and Time operations in sqlite3
+
+import sqlite3
+
+sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+table_name = 'my_table_3'	# name of the table to be created
+id_field = 'id' # name of the ID column
+date_col = 'date' # name of the date column
+time_col = 'time'# name of the time column
+date_time_col = 'date_time' # name of the date & time column
+field_type = 'TEXT'  # column data type
+
+# Connecting to the database file
+conn = sqlite3.connect(sqlite_file)
+c = conn.cursor()
+
+# Creating a new SQLite table with 1 column
+c.execute('CREATE TABLE {tn} ({fn} {ft} PRIMARY KEY)'\
+        .format(tn=table_name, fn=id_field, ft=field_type))
+
+
+# 1) Adding a new column to save date insert a row with the current date 
+# in the following format: YYYY-MM-DD
+# e.g., 2014-03-06
+c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}'"\
+         .format(tn=table_name, cn=date_col))
+# insert a new row with the current date and time, e.g., 2014-03-06
+c.execute("INSERT INTO {tn} ({idf}, {cn}) VALUES('some_id1', DATE('now'))"\
+         .format(tn=table_name, idf=id_field, cn=date_col))
+
+
+# 2) Adding a new column to save date and time and update with the current time
+# in the following format: HH:MM:SS
+# e.g., 16:26:37
+c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}'"\
+         .format(tn=table_name, cn=time_col))
+# update row for the new current date and time column, e.g., 2014-03-06 16:26:37
+c.execute("UPDATE {tn} SET {cn}=TIME('now') WHERE {idf}='some_id1'"\
+         .format(tn=table_name, idf=id_field, cn=time_col))
+
+# 3) Adding a new column to save date and time and update with current date-time
+# in the following format: YYYY-MM-DD HH:MM:SS
+# e.g., 2014-03-06 16:26:37
+c.execute("ALTER TABLE {tn} ADD COLUMN '{cn}'"\
+         .format(tn=table_name, cn=date_time_col))
+# update row for the new current date and time column, e.g., 2014-03-06 16:26:37
+c.execute("UPDATE {tn} SET {cn}=(CURRENT_TIMESTAMP) WHERE {idf}='some_id1'"\
+         .format(tn=table_name, idf=id_field, cn=date_time_col))
+
+# Database should now look like this:
+# id         date           time        date_time
+# "some_id1" "2014-03-06"   "16:42:30"  "2014-03-06 16:42:30"
+
+# 4) Retrieve all IDs of entries between 2 date_times
+c.execute("SELECT {idf} FROM {tn} WHERE {cn} BETWEEN '2013-03-06 10:10:10' AND '2015-03-06 10:10:10'".\
+    format(idf=id_field, tn=table_name, cn=date_time_col))
+all_date_times = c.fetchall()
+print('4) all entries between ~2013 - 2015:', all_date_times)
+
+# 5) Retrieve all IDs of entries between that are older than 1 day and 12 hrs
+c.execute("SELECT {idf} FROM {tn} WHERE DATE('now') - {dc} >= 1 AND DATE('now') - {tc} >= 12".\
+    format(idf=id_field, tn=table_name, dc=date_col, tc=time_col))
+all_1day12hrs_entries = c.fetchall()
+print('5) entries older than 1 day:', all_1day12hrs_entries)
+
+# Committing changes and closing the connection to the database file
+conn.commit()
+conn.close()

sqlite3_howto/code/get_columnnames.py

@@ -0,0 +1,24 @@
+# Sebastian Raschka, 2014
+# Getting column names of an SQLite database table
+
+import sqlite3
+
+sqlite_file = 'my_first_db.sqlite'
+table_name = 'my_table_3'
+
+# Connecting to the database file
+conn = sqlite3.connect(sqlite_file)
+c = conn.cursor()
+
+# Retrieve column information
+# Every column will be represented by a tuple with the following attributes:
+# (id, name, type, notnull, default_value, primary_key)
+c.execute('PRAGMA TABLE_INFO({})'.format(table_name))
+
+# collect names in a list
+names = [tup[1] for tup in c.fetchall()]
+print(names)
+# e.g., ['id', 'date', 'time', 'date_time']
+
+# Closing the connection to the database file
+conn.close()

sqlite3_howto/code/print_db_info.py

@@ -0,0 +1,91 @@
+# Sebastian Raschka 2014
+# Prints Information of a SQLite database.
+
+# E.g.,
+#
+"""
+Total rows: 1
+
+Column Info:
+ID, Name, Type, NotNull, DefaultVal, PrimaryKey
+(0, 'id', 'TEXT', 0, None, 1)
+(1, 'date', '', 0, None, 0)
+(2, 'time', '', 0, None, 0)
+(3, 'date_time', '', 0, None, 0)
+
+Number of entries per column:
+date: 1
+date_time: 1
+id: 1
+time: 1
+"""
+
+import sqlite3
+
+def connect(sqlite_file):
+    """ Make connection to an SQLite database file """
+    conn = sqlite3.connect(sqlite_file)
+    c = conn.cursor()
+    return conn, c
+
+def close(conn):
+    """ Commit changes and close connection to the database """
+    #conn.commit()
+    conn.close()
+
+def total_rows(cursor, table_name, print_out=False):
+    """ Returns the total number of rows in the database """
+    c.execute('SELECT COUNT(*) FROM {}'.format(table_name))
+    count = c.fetchall()
+    if print_out:
+        print('\nTotal rows: {}'.format(count[0][0]))
+    return count[0][0]
+
+def table_col_info(cursor, table_name, print_out=False):
+    """ 
+       Returns a list of tuples with column informations:
+      (id, name, type, notnull, default_value, primary_key)
+    
+    """
+    c.execute('PRAGMA TABLE_INFO({})'.format(table_name))
+    info = c.fetchall()
+    
+    if print_out:
+        print("\nColumn Info:\nID, Name, Type, NotNull, DefaultVal, PrimaryKey")
+        for col in info:
+            print(col)
+    return info
+
+def values_in_col(cursor, table_name, print_out=True):
+    """ Returns a dictionary with columns as keys and the number of not-null 
+        entries as associated values.
+    """
+    c.execute('PRAGMA TABLE_INFO({})'.format(table_name))
+    info = c.fetchall()
+    col_dict = dict()
+    for col in info:
+        col_dict[col[1]] = 0
+    for col in col_dict:
+        c.execute('SELECT ({0}) FROM {1} WHERE {0} IS NOT NULL'.format(col, table_name))
+        # In my case this approach resulted in a better performance than using COUNT
+        number_rows = len(c.fetchall())
+        col_dict[col] = number_rows
+    if print_out:
+        print("\nNumber of entries per column:")
+        for i in col_dict.items():
+            print('{}: {}'.format(i[0], i[1]))
+    return col_dict
+
+
+if __name__ == '__main__':
+
+    sqlite_file = 'my_first_db.sqlite'
+    table_name = 'my_table_3'
+
+    conn, c = connect(sqlite_file)
+    total_rows(c, table_name, print_out=True)
+    table_col_info(c, table_name, print_out=True)
+    values_in_col(c, table_name, print_out=True) # slow on large data bases
+    
+    close(conn)
+

sqlite3_howto/code/selecting_entries.py

@@ -0,0 +1,51 @@
+# Sebastian Raschka, 2014
+# Selecting rows from an existing SQLite database
+
+import sqlite3
+
+sqlite_file = 'my_first_db.sqlite'    # name of the sqlite database file
+table_name = 'my_table_2'	# name of the table to be queried
+id_column = 'my_1st_column'
+some_id = 123456
+column_2 = 'my_2nd_column'
+column_3 = 'my_3rd_column'    
+
+# Connecting to the database file
+conn = sqlite3.connect(sqlite_file)
+c = conn.cursor()
+
+# 1) Contents of all columns for row that match a certain value in 1 column
+c.execute('SELECT * FROM {tn} WHERE {cn}="Hi World"'.\
+        format(tn=table_name, cn=column_2))
+all_rows = c.fetchall()
+print('1):', all_rows)
+
+# 2) Value of a particular column for rows that match a certain value in column_1 
+c.execute('SELECT ({coi}) FROM {tn} WHERE {cn}="Hi World"'.\
+        format(coi=column_2, tn=table_name, cn=column_2))
+all_rows = c.fetchall()
+print('2):', all_rows)
+
+# 3) Value of 2 particular columns for rows that match a certain value in 1 column
+c.execute('SELECT {coi1},{coi2} FROM {tn} WHERE {coi1}="Hi World"'.\
+        format(coi1=column_2, coi2=column_3, tn=table_name, cn=column_2))
+all_rows = c.fetchall()
+print('3):', all_rows)
+
+# 4) Selecting only up to 10 rows that match a certain value in 1 column
+c.execute('SELECT * FROM {tn} WHERE {cn}="Hi World" LIMIT 10'.\
+        format(tn=table_name, cn=column_2))
+ten_rows = c.fetchall()
+print('4):', ten_rows)
+
+# 5) Check if a certain ID exists and print its column contents
+c.execute("SELECT * FROM {tn} WHERE {idf}=?".\
+        format(tn=table_name, cn=column_2, idf=id_column), (123456,))
+id_exists = c.fetchone()
+if id_exists:
+    print('5): {}'.format(id_exists))
+else:
+    print('5): {} does not exist'.format(some_id))
+
+# Closing the connection to the database file
+conn.close()

sqlite3_howto/code/update_or_insert_records.py

@@ -0,0 +1,35 @@
+# Sebastian Raschka, 2014
+# Update records or insert them if they don't exist.
+# Note that this is a workaround to accomodate for missing
+# SQL features in SQLite.
+
+import sqlite3
+
+sqlite_file = 'my_first_db.sqlite'
+table_name = 'my_table_2'
+id_column = 'my_1st_column'
+column_name = 'my_2nd_column'
+
+# Connecting to the database file
+conn = sqlite3.connect(sqlite_file)
+c = conn.cursor()
+
+
+# A) Inserts an ID with a specific value in a second column 
+try:
+    c.execute("INSERT INTO {tn} ({idf}, {cn}) VALUES (123456, 'test')".\
+        format(tn=table_name, idf=id_column, cn=column_name))
+except sqlite3.IntegrityError:
+    print('ERROR: ID already exists in PRIMARY KEY column {}'.format(id_column))
+
+# B) Tries to insert an ID (if it does not exist yet)
+# with a specific value in a second column 
+c.execute("INSERT OR IGNORE INTO {tn} ({idf}, {cn}) VALUES (123456, 'test')".\
+        format(tn=table_name, idf=id_column, cn=column_name))
+
+# C) Updates the newly inserted or pre-existing entry            
+c.execute("UPDATE {tn} SET {cn}=('Hi World') WHERE {idf}=(123456)".\
+        format(tn=table_name, cn=column_name, idf=id_column))
+
+conn.commit()
+conn.close()

sqlite3_howto/code/updating_rows.py

@@ -0,0 +1,50 @@
+# Sebastian Raschka, 2014
+# Updating rows in an existing SQLite database
+
+import sqlite3
+
+sqlite_file = ''
+table_name = ''
+column_name_1 = ''  
+column_name_2 = ''
+column_name_3 = ''
+value_1 = 'hello world'
+value_2 = 12345
+
+conn = sqlite3.connect(sqlite_file)
+c = conn.cursor()
+
+
+# A.1) Updating all rows for a single column
+
+c.execute('UPDATE {dn} SET {cn1}={v1}'.\
+        format(dn=table_name, cn1=column_name_1, v1=value1)
+
+
+# A.2) Updating all rows for 2 columns (same for multiple columns)
+
+c.execute('UPDATE {dn} SET {cn1}={v1}, {cn2}={v2}'.\
+        format(dn=table_name, cn1=column_name_1, cn2=column_name_2,
+               v1=value1, v2=value2)
+
+
+
+
+# B.1) Updating specific rows that meet a certain criterion
+# here: update column_1 with value_1 if row has value_2 in column_2
+
+c.execute('UPDATE {dn} SET {cn1}={v1} WHERE {cn2}={v2}'.\
+        format(dn=table_name, cn1=column_name_1, v1=value1)
+
+
+# B.2) Updating specific rows that meet multiple criteria
+# here: update column_1 with value_1 
+#    if row has value_2 in column_2
+#    and if row has value = 1 in column_3
+
+c.execute('UPDATE {dn} SET {cn1}={v1} WHERE {cn2}={v2} AND {cn3}=1'.\
+        format(dn=table_name, cn1=column_name_1, v1=value1, cn3=column_name_3)
+
+
+conn.commit()
+conn.close()

sqlite3_howto/code/write_from_sqlite.py

@@ -0,0 +1,102 @@
+import sqlite3
+
+def create_col_index(db_name, table_name, column_name, index_name):
+    '''
+    Creates a column index on a SQLite table.
+    
+    Keyword arguments:
+        db_name (str): Path of the .sqlite database file.
+        table_name (str): Name of the target table in the SQLite file.
+        condition (str): Condition for querying the SQLite database table.
+        column_name (str): Name of the column for which the index is created.
+
+    '''
+
+    # Connecting to the database file
+    conn = sqlite3.connect(db_name)
+    c = conn.cursor()
+
+    # Creating the index
+    c.execute('CREATE INDEX {} ON {} ({})'.format(index_name, table_name, column_name))
+
+    # Save index and close the connection to the database
+    conn.commit()
+    conn.close()
+
+
+
+def drop_col_index(db_name, index_name):
+    '''
+    Drops a column index from a SQLite table.
+    
+    Keyword arguments:
+        db_name (str): Path of the .sqlite database file.
+        table_name (str): Name of the target table in the SQLite file.
+        condition (str): Condition for querying the SQLite database table.
+        column_name (str): Name of the column for which the index is dropped.
+
+    '''
+
+    # Connecting to the database file
+    conn = sqlite3.connect(db_name)
+    c = conn.cursor()
+
+    # Drops the index
+    c.execute('DROP INDEX {}'.format(index_name))
+
+    # Save index and close the connection to the database
+    conn.commit()
+    conn.close()
+
+
+
+def write_from_query(db_name, table_name, condition, content_column, out_file, fetchmany=False):
+    '''
+    Writes contents from a SQLite database column to an output file
+    
+    Keyword arguments:
+        db_name (str): Path of the .sqlite database file.
+        table_name (str): Name of the target table in the SQLite file.
+        condition (str): Condition for querying the SQLite database table.
+        content_column (str): Name of the column that contains the content for the output file.
+        out_file (str): Path of the output file that will be written.
+
+    '''
+    # Connecting to the database file
+    conn = sqlite3.connect(db_name)
+    c = conn.cursor()
+
+    # Querying the database and writing the output file
+
+
+    # A) using .fetchmany(); recommended for larger databases
+    if fetchmany:
+        c.execute('SELECT ({}) FROM {} WHERE {}'.format(content_column, table_name, condition))
+        with open(out_file, 'w') as outf:
+            results = c.fetchmany(fetchmany)
+            while results:
+                for row in results:
+                    outf.write(row[0])
+                results = c.fetchmany(fetchmany)
+
+    # B) simple .execute() loop
+    else:
+        c.execute('SELECT ({}) FROM {} WHERE {}'.format(content_column, table_name, condition))
+        with open(out_file, 'w') as outf:
+            for row in c:
+                outf.write(row[0])
+
+    # Closing the connection to the database
+    conn.close()
+
+if __name__ == '__main__':
+    write_from_query(
+        db_name='my_db.sqlite',
+        table_name='my_table',
+        condition='variable1=1 AND variable2<=5 AND variable3="Zinc_Plus"',
+        content_column='variable4',
+        out_file='sqlite_out.txt'
+    )
+        
+
+