Question

I am looking for an sqlite3 command that let’s me select entries given by a tuple, let me explain with an example:

Here is my data:

my_data = [(1,8),(2,4),(3,5),(4,7),(5,13)]

and I am trying to extract entries who’s first values are either 1,2 or 4; hence, my desired output is:

[(1, 8), (2, 4), (4, 7)]

I can achieve that with a code below; however, I think that my code is not optimal:

import sqlite3

my_data = [(1,8),(2,4),(3,5),(4,7),(5,13)]

key_indexes = (1,2,4)

conn = sqlite3.connect(':memory:')

c = conn.cursor()

c.execute('''CREATE TABLE my_table
          (val_1 INTEGER, val_2 INTEGER)''')

for entry in my_data:
    c.execute('''INSERT INTO my_table VALUES(?,?)''',entry)

conn.commit()

result = []

for ind in key_indexes:
    c.execute('''SELECT* FROM my_table WHERE val_1 = ?''', (ind,))
    temp_res = c.fetchall()

    result.extend(temp_res)

I am looking for a code that can replace the for loop at the and with an sqlite3 command.
I want to stick (1,2,4) somewhere in this line:

c.execute('''SELECT* FROM my_table WHERE val_1 = ?''', (ind,))

instead of doing a for loop.
Thank You in Advance

Answer 1

To replace the last for-loop you can build up the list of indexes/indices in a string and hit the database just once.
Please note that this is a two-step process, and not vulnerable — in and of itself — to SQL injection attacks.

my_query = '''SELECT val_1, val_2
              FROM   my_table 
              WHERE  val_1 IN ({:s});'''.format(",".join("?"*len(key_indexes)))
# -> 'SELECT val_1, val_2 FROM my_table WHERE val_1 IN (?,?,?);'
c.execute(myquery, ind).fetchall()

Additionally:
You didn’t directly ask about this, but the first for loop and call to execute() could be reduced to a single call to executemany().
You should test which of the two options is faster because the DB-API doesn’t specify exactly how executemany() should be implemented; performance may differ across RDBMSs.

c.executemany('''INSERT INTO my_table VALUES (?,?);''', my_data)

You may read up on executemany() here: http://www.python.org/dev/peps/pep-0249/
For now, suffice it to say that it takes as the second argument a sequence of parameters.