IFNULL功能似乎對於MySQL中我

Question

IFNULL功能似乎並不爲我工作工作....當我執行此查詢

select t1.dAccHeader_id,t1.dAccHeaderName,t1.dAccHeaderAcronym, 
t2.dDesignationName as incharge1, 
t3.dDesignationName as incharge2,t4.dDesignationName as incharge3 
from tbl_accountheader as t1 
inner join tbl_designation_master as t2 on t2.dDesignation_id = t1.dPaymentIncharge_1 
inner join tbl_designation_master as t3 on t3.dDesignation_id = ifnull(t1.dPaymentIncharge_2,'0') 
inner join tbl_designation_master as t4 on t4.dDesignation_id = ifnull(t1.dPaymentIncharge_3,'0') 
and t1.dCollege_id='1' 
and t1.dIsDelete='0' 

這裏是我的表，

My Table http://www.freeimagehosting.net/uploads/cf77e5a156.jpg

任何sugesstion ...

Answer 1

您可以嘗試使用coalesce功能

inner join tbl_designation_master as t3 
     on t3.dDesignation_id = coalesce(t1.dPaymentIncharge_2,'0') 

如果你的id是一個數字，你也可以刪除該帖：

coalesce(t1.dPaymentIncharge_2, 0) 

檢查還如果你的t1.dPaymentIncharge_1可以爲空