当使用子查询查找具有匹配字段的所有先前记录的总数时,在只有 50k 条记录的表上性能很差。如果没有子查询,查询会在几毫秒内执行。对于子查询,执行时间超过一分钟。
对于此查询,结果必须:
Activity
======================
Id int Identifier
Address varchar(25)
ActionDate datetime2
Process varchar(50)
-- 7 other columns
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Id Address ActionDate (Time part excluded for simplicity)
===========================
99 000 2017-05-30
98 111 2017-05-30
97 000 2017-05-29
96 000 2017-05-28
95 111 2017-05-19
94 222 2017-05-30
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对于日期范围2017-05-29,以2017-05-30
Id Address ActionDate PriorCount
=========================================
99 000 2017-05-30 2 (3 total, 2 prior to ActionDate)
98 111 2017-05-30 1 (2 total, 1 prior to ActionDate) …Run Code Online (Sandbox Code Playgroud)