SELECT 字段作为 mytest WHERE mytest 为 NULL - 字段 "mytest" 未找到？

Question

我试图在 where 子句中使用选定字段的命名别名，但数据库抱怨无法找到该字段。

查询:

SELECT somefunction(myfield) as mytest, myotherfield as mytest2
FROM database.table
WHERE mytest IS NULL OR mytest2 IS NULL

期望： 数据库将简单地测试 somefunction(myfield) 或 mytest 的结果是否为 NULL

结果：数据库找不到mytest或mytest2

有什么我遗漏的吗？为什么这样的东西不起作用？

Answer 1

SELECT somefunction(myfield) as mytest, myotherfield as mytest2 FROM table WHERE mytest IS NULL OR mytest2 IS NULL

编辑：抱歉 table。

可能重复：

Using column alias in WHERE clause of MySQL query produces an error

答案：

您只能在 GROUP BY、ORDER BY 或 HAVING 子句中使用列别名。

Standard SQL doesn't allow you to refer to a column alias in a WHERE clause. This restriction is imposed because when the WHERE code is executed, the column value may not yet be determined.

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

SELECT 字段作为 mytest WHERE mytest 为 NULL - 字段 "mytest" 未找到？

SELECT field as mytest WHERE mytest IS NULL - field "mytest" not found?

sql

db2