Python sqlite3 string variable in execute

问题

I try to execute this sqlite3 query in Python. I reduced the code to the minimum, sqlite.connect, etc works.

column = 'Pron_1_Pers_Sg'
goal = 'gender' 
constrain = 'Mann'


with con:
    cur = con.cursor()

    cur.execute("SELECT ? FROM Data where ?=?", (column, goal, constrain))
    con.commit()

    rows = cur.fetchall()

    for element in rows:
        values.append(element)

This returns an empty list. If I hardcode the strings, it works and returns values.

回答1:

Parameter markers can be used only for expressions, i.e., values. You cannot use them for identifiers like table and column names.

Use this:

cur.execute("SELECT "+column+" FROM Data where "+goal+"=?", (constrain,))

or this:

cur.execute("SELECT %s FROM Data where %s=?" % (column, goal), (constrain,))

(And don't commit before you have actually finished accessing the data.)

回答2:

Try this: c.execute("SELECT {idf} FROM Data WHERE {goal}".\ format(idf=column, goal=constrain))

回答3:

I was having quite a similar problem today. I am not sure, if this might solve your problem:

cur.execute("SELECT ? FROM Data where ?=?", (column, goal, constrain,))

Important is the last ,

Give it a try, this was the problem with my code - so maybe it helps you too. Sorry, for not being able to really explain why, as I am just learning myself and am into python/sqlite for some weeks.

来源：https://stackoverflow.com/questions/13880786/python-sqlite3-string-variable-in-execute