[python] How to use variables in SQL statement in Python?

Ok so I'm not that experienced in Python.

I have the following Python code:

cursor.execute("INSERT INTO table VALUES var1, var2, var3,")

where var1 is an integer, var2 & var3 are strings.

How can I write the variable names without python including them as part of the query text?

Many ways. DON'T use the most obvious one (%s with %) in real code, it's open to attacks.

Here copy-paste'd from pydoc of sqlite3:

# Never do this -- insecure!
symbol = 'RHAT'
c.execute("SELECT * FROM stocks WHERE symbol = '%s'" % symbol)

# Do this instead
t = ('RHAT',)
c.execute('SELECT * FROM stocks WHERE symbol=?', t)
print c.fetchone()

# Larger example that inserts many records at a time
purchases = [('2006-03-28', 'BUY', 'IBM', 1000, 45.00),
             ('2006-04-05', 'BUY', 'MSFT', 1000, 72.00),
             ('2006-04-06', 'SELL', 'IBM', 500, 53.00),
            ]
c.executemany('INSERT INTO stocks VALUES (?,?,?,?,?)', purchases)

More examples if you need:

# Multiple values single statement/execution
c.execute('SELECT * FROM stocks WHERE symbol=? OR symbol=?', ('RHAT', 'MSO'))
print c.fetchall()
c.execute('SELECT * FROM stocks WHERE symbol IN (?, ?)', ('RHAT', 'MSO'))
print c.fetchall()
# This also works, though ones above are better as a habit as it's inline with syntax of executemany().. but your choice.
c.execute('SELECT * FROM stocks WHERE symbol=? OR symbol=?', 'RHAT', 'MSO')
print c.fetchall()
# Insert a single item
c.execute('INSERT INTO stocks VALUES (?,?,?,?,?)', ('2006-03-28', 'BUY', 'IBM', 1000, 45.00))

The syntax for providing a single value can be confusing for inexperienced Python users.

Given the query

INSERT INTO mytable (fruit) VALUES (%s)

The value passed to cursor.execute must still be a tuple even though it is a singleton, so we must provide a single element tuple, like this: (value,).

cursor.execute("""INSERT INTO mytable (fruit) VALUES (%s)""", ('apple',))

Different implementations of the Python DB-API are allowed to use different placeholders, so you'll need to find out which one you're using -- it could be (e.g. with MySQLdb):

cursor.execute("INSERT INTO table VALUES (%s, %s, %s)", (var1, var2, var3))

or (e.g. with sqlite3 from the Python standard library):

cursor.execute("INSERT INTO table VALUES (?, ?, ?)", (var1, var2, var3))

or others yet (after VALUES you could have (:1, :2, :3) , or "named styles" (:fee, :fie, :fo) or (%(fee)s, %(fie)s, %(fo)s) where you pass a dict instead of a map as the second argument to execute). Check the paramstyle string constant in the DB API module you're using, and look for paramstyle at http://www.python.org/dev/peps/pep-0249/ to see what all the parameter-passing styles are!

Meanwhile there is another way of how to do it with f-strings:

cursor.execute(f"INSERT INTO table VALUES {var1}, {var2}, {var3},")

http://www.amk.ca/python/writing/DB-API.html

Be careful when you simply append values of variables to your statements: Imagine a user naming himself ';DROP TABLE Users;' -- That's why you need to use sql escaping, which Python provides for you when you use the cursor.execute in a decent manner. Example in the url is:

cursor.execute("insert into Attendees values (?, ?, ?)", (name,
seminar, paid) )