Question

I am writing a nested MySQL query where a subquery returns more than one row and hence the query can not be executed.

Can anyone suggest me a solution for this problem?

Thanks in advance.

Answer 1

An error about a subquery returning more than one value says to me that you’re attempting a straight value comparison, like this:

WHERE col = (SELECT col2 FROM TABLE_2)

The solution depends on the data coming from the subquery – do you want the query to use all the values being returned? If yes, then change the equals sign for an IN:

WHERE col IN (SELECT col2 FROM TABLE_2)

Otherwise, you need to correct the subquery so it only ever returns one value. The MAX or MIN aggregate functions are a possibliity – they’ll return the highest or lowest value. It could just be a matter of correlating the subquery:

  FROM TABLE_1 t1
WHERE t1.col = (SELECT MAX(t2.col2)
                           FROM TABLE_2 t2
                         WHERE t2.fk_col = t1.id)  -- correlated example

As Tabhaza points out, a subquery generally doesn’t return more than one column (though some databases support tuple matching), in which case you need to define a derived table/inline view and join to it.

Would’ve been nice to have more information on the issue you’re having…