SQL 語句case when

簡介

case when 一般有兩種書寫方式，多用於查詢判斷

1.

case  列名
when  ''  then '空'
when  '1' then '成功'
when  '2' then '失敗'
else '其他'
end as '列名'

2.

case  
when 列名 is null then ''
when 列名 ='1' then '成功'
when 列名 ='2' then '失敗'
else '未知' 
end as '列名'

實例

  
  select a.Base_Code,a.BaseName,case when  LEN(d.Spell) >=3 then rtrim(d.Spell)+' 長度大於等於3' else  rtrim(d.Spell)+' 長度小於3' end  as '拼音碼',a.style,a.odate,case b.QR_code  when '' then '錯誤' else b.QR_code end as '二維碼' from [WlData].[dbo].[Tbl_OperateInventory] as a
   inner join Tbl_QRManage as b on a.QR_Code = b.QR_code 
   inner join Tbl_dic_BaseInfo as c on a.Base_Code = c.Base_Code
   inner join Tbl_dic_Alias as d on a.Base_Code  = d.AliasCode   where a.StockType='g'

 結論  null的判斷只能  通過第二種方法去判斷