"WITH"子句的 SQL 语法错误

Question

在 WHERE 子句中使用WITH 别名时遇到奇怪的问题。 问题SQL语句:

WITH CROOM AS (SELECT id FROM classroom WHERE floor = 1)
SELECT DISTINCT teacher_id
FROM timetable
WHERE classroom_id IN CROOM;

错误是ORA-00904:“CROOM”:无效标识符

虽然这两个语义相似的语句都效果很好。

SELECT DISTINCT teacher_id
FROM timetable
WHERE classroom_id IN (SELECT id FROM classroom WHERE floor = 1);

WITH CROOM AS (SELECT id FROM classroom WHERE floor = 1)
SELECT DISTINCT T.teacher_id 
FROM timetable T JOIN CROOM ON (T.classroom_id = CROOM.id);

为什么它无法识别 WHERE 中的别名，而在 FROM 子句中接受别名？

Answer 1

您应该使用 CROOM 作为表格。例如你可以这样写:

WITH CROOM AS (SELECT id FROM classroom WHERE floor = 1)
SELECT DISTINCT teacher_id
FROM timetable
WHERE classroom_id IN (select id from CROOM);