how to safely generate a SQL LIKE statement using

问题:

I am trying to assemble the following SQL statement using python's db-api:

SELECT x FROM myTable WHERE x LIKE 'BEGINNING_OF_STRING%';

where BEGINNING_OF_STRING should be a python var to be safely filled in through the DB-API. I tried

beginningOfString = 'abc'

cursor.execute('SELECT x FROM myTable WHERE x LIKE '%s%', beginningOfString) 
cursor.execute('SELECT x FROM myTable WHERE x LIKE '%s%%', beginningOfString)

I am out of ideas; what is the correct way to do this?

回答1:

It's best to separate the parameters from the sql if you can. Then you can let the db module take care of proper quoting of the parameters.

sql='SELECT x FROM myTable WHERE x LIKE %s'
args=[beginningOfString+'%']
cursor.execute(sql,args)

回答2:

EDIT:

As Brian and Thomas noted, the far better way to do this would be to use:

beginningOfString += '%'
cursor.execute("SELECT x FROM myTable WHERE x LIKE ?", (beginningOfString,) )

since the first method leaves you open to SQL injection attacks.

---

Left in for history:

Try:

cursor.execute("SELECT x FROM myTable WHERE x LIKE '%s%%'" % beginningOfString)

回答3:

Take note of Sqlite3 documentation:

Usually your SQL operations will need to use values from Python variables. You shouldn’t assemble your query using Python’s string operations because doing so is insecure; it makes your program vulnerable to an SQL injection attack.

Instead, use the DB-API’s parameter substitution. Put ? as a placeholder wherever you want to use a value, and then provide a tuple of values as the second argument to the cursor’s execute() method. (Other database modules may use a different placeholder, such as %s or :1.) For example:

# Never do this -- insecure!
symbol = 'IBM'
c.execute("... where symbol = '%s'" % symbol)

# Do this instead
t = (symbol,)
c.execute('select * from stocks where symbol=?', t)

# Larger example
for t in [('2006-03-28', 'BUY', 'IBM', 1000, 45.00),
          ('2006-04-05', 'BUY', 'MSOFT', 1000, 72.00),
          ('2006-04-06', 'SELL', 'IBM', 500, 53.00),
         ]:
    c.execute('insert into stocks values (?,?,?,?,?)', t)

I think you want this:

cursor.execute('SELECT x FROM myTable WHERE x LIKE '%?%', (beginningOfString,) )