SQL 查询 'NOT IN' 与 'Join'

Question

NOT IN 与使用 JOIN

SELECT  COUNT(*)
FROM TBL_A AS A
WHERE A.MailDatId = 185208
AND SUBSTRING(A.PIMBRecord,3,3) NOT IN (SELECT B.ServiceTypeId FROM TBL_B AS B WHERE B.IsStandard = 1);

 SELECT COUNT(*) FROM TBL_A AS A 
    LEFT JOIN (SELECT B.ServiceTypeId FROM TBL_B AS B WHERE B.IsStandard = 1) C
    ON SUBSTRING(A.PIMBRecord,3,3) = C.ServiceTypeId
    WHERE A.MailDatId = 185208
    and C.ServiceTypeId IS NULL

我有上面两个查询，哪个更有效率？另外，如何测试 sql 服务器中查询的效率？

Answer 1

我实际上会为此推荐 not exists：

select count(*)
from tbl_a a
where
    a.mailDatId = 
    and not exists (
        select 1 
        from tbl_b as b 
        where b.isStandard = 1 and b.serviceTypeId = substring(a.PIMBRecord,3,3)
    )

理由：

NOT IN 不是空安全的，而 NOT EXISTS 是
JOINs 通常更适合您想要 return 来自另一个 table 的用例 - 这里不是这种情况

为了性能，您需要 tbl_b(serviceTypeId, isStandard)

上的索引

SQL 查询 'NOT IN' 与 'Join'

SQL query 'NOT IN' vs 'Join'

sql

tsql

sql-server

join

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