我想将两个选择
查询与UNION结合起来.
如何在第二个SELECT中使用第
一个SELECT的结果?
(SELECT carto_id_key FROM table1
WHERE tag_id = 16)
UNION
(SELECT * FROM table2
WHERE carto_id_key = <the carto_id result from above> )
使用
CTE在多个SELECT中重用子
查询的结果.
你需要Postgre
sql 8.4:
WITH x AS (SELECT carto_id_key FROM table1 WHERE tag_id = 16)
SELECT carto_id_key
FROM x
UNION ALL
SELECT t2.some_other_id_key
FROM x
JOIN table2 t2 ON t2.carto_id_key = x.carto_id_key
你很可能想要UNION ALL
而不是UNION.不排除重复,并且这种方式更快.