Question

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.

Answer 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.)