Python and MySQLdb: substitution of table resulting in syntax error

问题

I need to dynamically change tables and variables from time to time, so I wrote a python method like this:

    selectQ =\"\"\"SELECT * FROM  %s WHERE %s = %s;\"\"\" 
    self.db.execute(selectQ,(self.table,self.columnSpecName,idKey,))
    return self.db.store_result()

However this results in a syntax error exception. I tried debugging it so I printed the variables in the method and filled them in manually, and that worked. So I am not sure what I am doing wrong ?

Is it because I try to use a substitute for a table ?

Also how do I debug mysqldb so it prints the substituted query as a string ?

回答1:

Parameter substitution in the DB API is only for values - not tables or fields. You'll need to use normal string substitution for those:

selectQ ="""SELECT * FROM  %s WHERE %s = %%s;""" % (self.table,self.columnSpecName)
self.db.execute(selectQ,(idKey,))
return self.db.store_result()

Note that the value placeholder has a double % - this is so that it's left alone by the initial string substitution.

回答2:

Here is a full working example

def rtnwkpr(tick, table, col):

    import MySQLdb as mdb
    tickwild = tick + '%'       
    try:
        con = mdb.connect(host, user, password, db);
        cur = con.cursor()
        selectq = "SELECT price FROM %s WHERE %s LIKE %%s;" % (table, col)
        cur.execute(selectq,(tickwild))
        return cur.fetchall()

回答3:

You'll have to use string substitution to add the table and column names, the driver will only handle parameters.

Ed: NM, Daniel answered faster and more completely

回答4:

Did you mean to write:

selectQ = """SELECT * FROM %s WHERE %s = %s;""" % (self.table,self.columnSpecName,idKey) #maybe the idkey should be self.idkey? don't know the rest of the code

self.db.execute(selectQ)

and this is just a mistake with string formatting?

Btw why do you write explicit SQL for this kind of work? better use magical sqlalchemy for python sql manipulation..

来源：https://stackoverflow.com/questions/9394291/python-and-mysqldb-substitution-of-table-resulting-in-syntax-error

标签

python

mysql-python