sql - 在 PostgreSQL 中合并两个 SELECT 查询

Question

我想将两个选择查询与UNION.
如何SELECT在第二个中使用第一个的结果SELECT？

(SELECT carto_id_key FROM table1
    WHERE tag_id = 16)
UNION 
(SELECT * FROM table2
    WHERE carto_id_key = <the carto_id result from above> )

Answer 1

使用CTE在多个SELECT.

WITH cte AS (SELECT carto_id_key FROM table1 WHERE tag_id = 16)

SELECT carto_id_key
FROM   cte

UNION ALL
SELECT t2.some_other_id_key
FROM   cte
JOIN   table2 t2 ON t2.carto_id_key = ctex.carto_id_key

你很可能想要UNION ALL而不是UNION. 不排除重复项，并且这样更快。