如果我有这样的查询
SELECT date_trunc('day', assigndate)e,
count(CASE WHEN a.assigneeid = 65548
AND a.assigneeid IN
(SELECT userid
FROM groupmembers
WHERE groupid = 65553) THEN 1 ELSE NULL END) assigned,
count(CASE WHEN a.assigneeid = 65548
AND a.completedtime IS NOT NULL
AND a.assigneeid IN
(SELECT userid
FROM groupmembers
WHERE groupid = 65553) THEN 1 ELSE NULL END) completed
FROM ASSIGNMENT a
WHERE assigndate > CURRENT_TIMESTAMP - interval '20 days'
GROUP BY date_trunc('day',assigndate);
有问题的子查询是
SELECT userid
FROM groupmembers
WHERE groupid = 65553
那么由于子查询与父查询不相关
,它只会执行一次并使用缓存的结果。但由于子查询出现在查询中的 2 个位置,因此根据 SQL 计划
,它被计算两次。有没有办法缓存
该子查询的结果并在两个位置使用它?
子查询不能转换为连接,因为没有单个字段可以连接(而且它不能是无条件连接,因为那样计数会出错)
最佳答案
您可以使用公用表表达式 ( WITH
)
with cte as
(
SELECT userid FROM groupmembers WHERE groupid = 65553
)
SELECT
date_trunc('day', assigndate)e,
count(CASE WHEN a.assigneeid = 65548 AND a.assigneeid IN
(SELECT userid from cte) then 1 else null end) assigned,
...
关于sql - 如果一个不相关的子查询在查询中的几个地方重复出现,是否可以缓存它并重用结果?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13011280/