MYSQL - 子查询问题 - 不能重用表

Question

WITH t as (
SELECT *
            FROM scd p
            WHERE  p.modified_date > FROM_UNIXTIME(1593060230)
                AND ( p.main_id = 1
                OR FIND_IN_SET(1, p.mult_ids) <> 0 )
            ORDER BY modified_date DESC
            LIMIT 2 OFFSET 0
),
del as (
SELECT 
* 
FROM t WHERE (status <> 1 AND status <> 2)
),
w_del as (
SELECT 
* 
FROM t WHERE (status = 1 OR status = 2)
)
SELECT w_del.*, del.* FROM w_del,del;

How do I achieve this with normal sub queries. I am using MySQL 5.7 and can't use CTEs. Im getting can't reuse table error if I use UNION/sub-queries. Is there a way to achieve this without temporary tables?

Please help.

Answer 1

You can just plug in the code for each alias. . . and keep doing that until you are at the base tables:

SELECT w_del.*, del.*
FROM (SELECT t.*
      FROM (SELECT *
            FROM scd p
            WHERE p.modified_date > FROM_UNIXTIME(1593060230) AND
                  ( p.main_id = 1 OR FIND_IN_SET(1, p.mult_ids) <> 0 )
            ORDER BY modified_date DESC
            LIMIT 2 OFFSET 0
           ) t
       WHERE (status <> 1 AND status <> 2)
      ) w_del CROSS JOIN
     (SELECT t.*
      FROM (SELECT *
            FROM scd p
            WHERE p.modified_date > FROM_UNIXTIME(1593060230) AND
                  ( p.main_id = 1 OR FIND_IN_SET(1, p.mult_ids) <> 0 )
            ORDER BY modified_date DESC
            LIMIT 2 OFFSET 0
           ) t
       WHERE (status = 1 OR status = 2)
      ) del;

One critical point, though: The definition of t is using ORDER BY and LIMIT . If there are ties in the modified_date column, then the two subqueries could return different result sets. You have two choices to avoid a problem here:

1. Add additional keys to the ORDER BY to ensure that the sorting is stable (ie returns the same results each time because the combination of keys is unique).
2. Materialize the subquery using a temporary table.