SQL 语法错误 "WITH" 子句

Question

在 WHERE 子句中使用 WITH 别名时遇到一个奇怪的问题。 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": invalid identifier

虽然这两个语义相似的语句都很有效。

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);

为什么在 FROM 子句中接受别名却无法识别 WHERE 中的别名？

Answer 1

您应该将 CROOM 用作 table。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);