尝试优化这个T-SQL查询

Question

我有这个T-SQL查询，我想优化。

我不知道如何使所有其余的查询从"where DateLoad...."应该修改为。

看来我有可能使它更简单，但我不确定如何使它更简单。

select Employee_Number, 
DateLoad, 
min(Rate_1_Pay_Rate) as Rate_1_Pay_Rate,
min(Hourly_Rate) as Hourly_Rate, 
min(FLSA_Status) as FLSA_Status,  
min(Hire_Date) as Hire_Date, 
min(Employee_Type) as Employee_Type,
min(Status_Type) as Status_Type
from dbo.TableMain as hist
where DateLoad = (select min(DateLoad)
from dbo.TableMain as hist2 
where hist.Employee_Number = hist2.Employee_Number)
and Employee_Type = (select min(Employee_Type)
from dbo.TableMain as hist2 
where hist.Employee_Number = hist2.Employee_Number)
and Status_Type = (select min(Status_Type)
from dbo.TableMain as hist2 
where hist.Employee_Number = hist2.Employee_Number)
and Hire_Date = (select min(Hire_Date) 
from dbo.TableMain as hist2 
where hist.Employee_Number = hist2.Employee_Number) 
group by Employee_Number, DateLoad

Answer 1

如果不了解数据的更多上下文，我认为您可能无法真正获得基于5个单独列中的每个列的最小值的预期输出。让我们用一些数据来演示一下

TableMain
Employee_Number   DateLoad  Employee_Type  Status_Type  Hire_Date
1                 1/25      Z              D            1/21
1                 2/15      Y              A            1/21
1                 6/21      X              B            1/21

通过查看单个雇员的示例数据(看起来您的表将为单个人有多个条目)，如果我对每个相应列取MIN()，我将得到

Minimums          MINIMUM   MINIMUM        MINIMUM      MINIMUM
Employee_Number   DateLoad  Employee_Type  Status_Type  Hire_Date
1                 1/25      X              A            1/21

通过连接返回找到"single";包含这5个元素的记录不存在。

请编辑你的帖子，试着提供样本数据，以更好地说明你有数据和你正在寻找从它得到什么。简单的英文描述，以澄清，但编辑你的原始帖子，并提供额外的数据和背景。