连接多个SQL语句

Question

SELECT column_a1,column_b1,column_c1,column_d1,column_e1,column_f1,column_g1 
FROM mytable WHERE id=12 AND detectcolumn=1  

UNION ALL

SELECT column_a2,column_b2,column_c2,column_d2,column_e2,column_f2 
FROM mytable WHERE id=12 AND detectcolumn=2 

UNION ALL

SELECT column_a3,column_b3,column_c3,column_d3,column_e3,column_f3,column_g3
FROM mytable WHERE id=12 AND detectcolumn=3 

UNION ALL

SELECT column_a4 from mytable WHERE id=12 AND detectcolumn=4 

UNION ALL

SELECT column_a5 from mytable WHERE id=12 AND detectcolumn=5 

UNION ALL

SELECT column_a6 from mytable WHERE id=12 AND detectcolumn=6 

UNION ALL

SELECT column_a7 from mytable WHERE id=12 AND detectcolumn=7    

我该如何将所有这些sql语句合并为一个sql语句。我想根据detectcolumn的值从mytable中获取特定的列。

我尝试使用UNION ALL，但它给出错误ORA-01789：查询块的结果列数不正确

Answer 1

使用如下模式：

 select
   case detectcolumn
     when 4 then column_a4
     when 5 then column_a5
     when 6 then column_a6
   end
 from
   my_table
 where
   id           = 12 and
   detectcolumn in (4,5,6)