Question

以下语句执行时间差不多2分钟，当使用相同表格和视图的select语句略有不同时，结果相同：

SELECT
@NEW_CAREER_NUMBER = MAX(a.[career number])
FROM selecthr20.employee.[career history] a 
    INNER JOIN selecthr20.Employee.[Current Appointments As At Evaluation Date] b
        ON a.[appointment number] = b.[appointment number]  
    INNER JOIN Employee.[BSK Changes in Selected Period] c
        ON a.[career number] = c.[primary key number]
    INNER JOIN selecthr20.employee.[career history extra detail] d
        ON a.[career number] = d.[career number]
            AND c.[primary key number] = d.[career number]
where c.[primary key name] = 'Career Number'
and c.[audit date] < (Select max([audit date]) from Employee.[BSK Changes in Selected Period] where [primary key number] = @LATEST_CAREER_NUMBER)
and b.[person number] = @PERSON_ID

＆＃39; [所选期间的BSK变更] c＆＃39;是一种观点，其余的是表格。

Answer 1

你在d加入时有一个多余的条件试一试

SELECT
@NEW_CAREER_NUMBER = MAX(a.[career number])
FROM selecthr20.employee.[career history] a 
JOIN selecthr20.Employee.[Current Appointments As At Evaluation Date] b
      ON b.[appointment number] = a.[appointment number] 
     and b.[person number]      = @PERSON_ID  
JOIN selecthr20.employee.[career history extra detail] d
      ON d.[career number] = a.[career number] 
JOIN Employee.[BSK Changes in Selected Period] c
      ON c.[primary key number] = a.[career number] 
     and c.[primary key name]   = 'Career Number'
     and c.[audit date] < ( Select max([audit date])   
                              from Employee.[BSK Changes in Selected Period]
                             where [primary key number] = @LATEST_CAREER_NUMBER );

自然地在连接条件上加上索引

如果你在c join上有一个循环，那么使用一个变量作为审计日期
我会这样做 - 没有什么不好的方面

declare @auditdate DateTime = ( Select max([audit date]) 
                                  from Employee.[BSK Changes in Selected Period] 
                                 where [primary key number] = @LATEST_CAREER_NUMBER );

... 

and c.[audit date] < @auditdate

如何优化这个select语句？

1 个答案: