重构 COALESCE 比较

Question

在 WHERE 子句的 OR 部分，我有这样的内容：

COALESCE(Table2.FireDate, Table1.HireDate,'06/06/2079') = ISNULL(Table3.DeathDate,'06/06/2079')

我想看看有没有办法避免 COALESCE 调用并仍然获得相同的结果？如果可能的话，我希望获得一些性能。

Answer 1

我不确定性能会更好。但是您可以根据需要摆脱合并：

declare @fireDate date = null -- '01/20/2017'
declare @hireDate date = '01/20/2017'
declare @deathDate date = '01/20/2017'

if (COALESCE(@fireDate, @hireDate, '06/06/2079') = ISNULL(@deathDate, '06/06/2079'))
begin
    select '+'
end;


if(@fireDate is null and @hireDate is null and @deathDate is null)
   or (@fireDate = @deathDate)
   or (@fireDate is null and @hireDate = @deathDate) begin
    select '+'
end;

重构 COALESCE 比较

Refactoring a COALESCE comparison

sql

tsql

sqlperformance