Unknown column error in this COUNT MySQL statement?

Question

Error is

Unknown column 'num' in 'where' clause

SELECT COUNT(*) AS num, books_bookid
FROM bookgenre_has_books
WHERE num > 10
GROUP BY books_bookid

What am I doing wrong? Thanks.

Answer 1

WHERE clause cant see aliases,use HAVING.

It is not allowable to refer to a column alias in a WHERE clause, because the column value might not yet be determined when the WHERE clause is executed

http://dev.mysql.com/doc/refman/5.0/en/problems-with-alias.html

Answer 2

Try this, you should use the HAVING clause

SELECT COUNT(*) AS num, books_bookid
FROM bookgenre_has_books
GROUP BY books_bookid
HAVING COUNT(*) > 10

The SQL HAVING clause is used in combination with the SQL GROUP BY clause. It can be used in an SQL SELECT statement to filter the records that a SQL GROUP BY returns.