用于MySQL查询执行的python StringBuilder

Question

I am trying to query my database where one of the columns is a python variable:

weekNum = "week" + str(i)               #i is either 2, 3, 4, 5
cur.execute("select %s from golden_table where nGram = %s and hash_tag = %s", (weekNum, tup[0], tup[1]))

Note that the SQL table: golden_table includes the 4 columns: week2 week3 week4 week5 . However, python or MySQL is not treating the value of weekNum as a column. Instead what is returned from the query is the value "weeki." where i is as above. In Java, I know the way around this is the StringBuilder class.

1. What is the equivalent way of solving this problem in python?
2. What is a better way to solve this in python?

All help is appreciated, and let me know if you need more information.

Answer 1

If your python version is recent (2.6+). You could use format.

weekNum = "week" + str(i)               #i is either 2, 3, 4, 5
query = "select {0} from golden_table where nGram = %s and hash_tag = %s".format(weekNum)
cur.execute(query, (tup[0], tup[1]))

Answer 2

Parameter replacement in execute is for values, not fieldnames. You'll need to use normal string interpolation for that. So:

sql = "select %s from golden_table where nGram = %%s and hash_tag = %%s" % weekNum
cur.execute(sql, tup)

Note the double percents in the first statement so that they pass through the string interpolation unscathed.