Note that the use of the Case function in transact-SQL leads to different result sets.

Select a. GCMC as fname, A. jsdw as fowner,Case
When B. FID is null then-1 else B. FID end as farea,
A. content as fcontent, A. updatetime as ftime, null as fhref, A. deleted as fisdel

From z_bidding a left join ccic_area B on charindex (B. fname, A. areaid)> 0

And

Select a. GCMC as fname, A. jsdw as fowner,Case B. FID
When null then-1 else B. FID end as farea,
A. content as fcontent, A. updatetime as ftime, null as fhref, A. deleted as fisdel

From z_bidding a left join ccic_area B on charindex (B. fname, A. areaid)> 0

The execution results are different.

A. Easy to use Case Function Select Statement

Use Adventureworks;
Go
Select Productnumber, category =
Case Productline
When   ' R '   Then   ' Road '
When   ' M '   Then   ' Mountain '
When   ' T '   Then   ' Touring '
When   ' S '   Then   ' Other sale items '
Else   ' Not for sale '
End ,
Name
From Production. Product
Order   By Productnumber;
Go


B. Easy to use Case Functions and Case Search function Select Statement

Use Adventureworks;
Go
Select Productnumber, name, ' Price Range '   =  
Case  
When Listprice = 0   Then   ' MFG item-not for resale '
When Listprice <   50   Then   ' Under $50 '
When Listprice > =   50   And Listprice <   250   Then   ' Under$ 250 '
When Listprice > =   250   And Listprice <   1000   Then   ' Under$ 1000 '
Else   ' Over $1000. '
End
From Production. Product
Order   By Productnumber;
Go