此COUNT个MySQL语句中的未知列错误? [英] Unknown column error in this COUNT MySQL statement?

问题描述

错误是

"where"子句中的未知列"num"

Unknown column 'num' in 'where' clause

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

我做错了什么?谢谢.

推荐答案

WHERE子句无法看到别名，请使用HAVING.

WHERE clause cant see aliases,use HAVING.

不允许在WHERE子句中引用列别名，因为执行WHERE子句时可能尚未确定列值

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

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