SELECT INTO变量

Question

我有很多命令，如：

DELETE FROM table1 WHERE user_id IN (SELECT id FROM users WHERE email LIKE 'abc%');
DELETE FROM table2 WHERE user_id IN (SELECT id FROM users WHERE email LIKE 'abc%');
DELETE FROM table3 WHERE user_id IN (SELECT id FROM users WHERE email LIKE 'abc%');

如何通过变量/ list / array / set中的提取来优化它？

SELECT id FROM users WHERE email LIKE 'abc%'

Answer 1

如果你的目标是只编写一次只删除一个用户的条件，你可以使用修改CTE的数据：

with user_list as (
   select id
   from users
   where email like 'abc%'
), delete_1 as (
   delete from table_1 where user_id in (select id from user_list)
), delete_1  as (
   delete from table_2 where user_id in (select id from user_list)
) 
delete from table_3 where user_id in (select id from user_list);

您仍然需要为每次删除重复select ...，但条件需要删除的内容只需在您的对帐单中删除一次。

Answer 2

您可以将临时表创建为

CREATE TEMP TABLE user_for_delete as
SELECT id 
FROM users 
WHERE email 
LIKE 'abc%';

以及任何其他条件

INSERT INTO user_for_delete (id)
SELECT id 
FROM users 
WHERE email 
LIKE 'cdb%';

最后从table1,2,3

中删除

DELETE FROM table1 t
USING user_for_delete u
WHERE u.id = t.user_id

Answer 3

使用data-modifying CTEs之类的@a_horse suggested。但是从DELETE statements with the USING clause中的第一个CTE加入派生表。这有点短而快：

WITH sel  AS (SELECT id FROM users WHERE email LIKE 'abc%')
,    del1 AS (DELETE FROM table_1 t USING sel WHERE t.user_id = sel.id)
,    del2 AS (DELETE FROM table_2 t USING sel WHERE t.user_id = sel.id) 
              DELETE FROM table_3 t USING sel WHERE t.user_id = sel.id;