MYSQL5下查询语句CASE WHEN 子查询的使用

SQL语句如下:

根据表中某个字段的值 来进行判断,分别查询B表或C表中的字段值。

select

 purchase.psort_Id,
 (case
   when quote_type = 'PC' or quote_type = 'TD' THEN
    (select purchase_title
       from df_purchase_demand pd
      where pd.ps_id = quot.master_id limit 1)
   when quote_type = 'IV' then
    (select inventory_Title
       from df_inventory dv
      where dv.ivt_id = quot.master_id limit 1)
 end) as item_title
  from df_quote quot
  left join df_purchase_demand purchase on quot.master_id = purchase.ps_id

 where 1 = 1
   and quot.site_Id is not null

 order by quot.create_time desc