sql - 基于其他列的值的不同列计数优化查询

Question

一定有更好的方法来写这个，但我只是不确定那是什么。基本上，我试图计算一列中的不同值，其中在单独的列中满足条件。我找到了这个link ，但不知道如何在这里应用它。

这是查询，我使用的是 SQL Server 2008R2

SELECT lot,
    (SELECT COUNT(DISTINCT d.pid) FROM invdet d WHERE upk = 0 and d.lot = [invdet].lot) as noUpk,
    (SELECT COUNT(DISTINCT d.pid) FROM invdet d WHERE upk = 1 and d.lot = [invdet].lot) as isUpk
FROM invdet
WHERE ([status] in ('PQ','P2','FA','F2','BH','RL','SC','LD','PS'))
GROUP BY lot
HAVING COUNT(CASE WHEN invdet.upk = 1 THEN 1 ELSE null END) > 0

Answer 1

您可以利用 COUNT DISTINCT 不计算 NULL 的事实来为您带来优势。为了检查所有行，请创建一个 WHERE EXISTS 子句，而不是将结果集限制为这些状态:

SELECT lot,
    COUNT(DISTINCT (CASE WHEN upk = 0 THEN pid ELSE NULL END)) as noUpk
    COUNT(DISTINCT (CASE WHEN upk = 1 THEN pid ELSE NULL END)) as isUpk
FROM invdet q
WHERE EXISTS
(
    SELECT 1 
    FROM invdet i 
    WHERE i.[status] in ('PQ','P2','FA','F2','BH','RL','SC','LD','PS')
    AND i.lot = q.lot
)
GROUP BY lot
HAVING COUNT(CASE WHEN upk = 1 THEN 1 ELSE null END) > 0

---

您还可以有效地将 HAVING 子句移动到 WHERE EXISTS 子句中，这可能会更快，从而导致:

SELECT lot,
    COUNT(DISTINCT (CASE WHEN upk = 0 THEN pid ELSE NULL END)) as noUpk
    COUNT(DISTINCT (CASE WHEN upk = 1 THEN pid ELSE NULL END)) as isUpk
FROM invdet q
WHERE EXISTS
(
    SELECT 1 
    FROM invdet i 
    WHERE i.[status] in ('PQ','P2','FA','F2','BH','RL','SC','LD','PS')
    AND i.lot = q.lot
)
WHERE EXISTS
(
    SELECT 1 
    FROM invdet i 
    WHERE i.upk = 1 
    AND i.lot = q.lot
)
GROUP BY lot