mysql - 不能 UNION ALL 两个等价的查询吗？

Question

我有一个工作查询需要重复几次，但是我在 UNION ALL 上遇到语法错误:

工作查询:

set @num := 0, @group := '';

select person, `group`, age
from 
(
   select person, `group`, age,
      @num := if(@group = `group`, @num + 1, 1) as row_number,
      @group := `group` as dummy
  from mytable
  order by `Group`, Age desc
) as x where x.row_number <= 2;

SQL FIDDLE

UNION ALL 失败(出现语法错误):

set @num := 0, @group := '';
(
select person, `group`, age
from 
(
   select person, `group`, age,
      @num := if(@group = `group`, @num + 1, 1) as row_number,
      @group := `group` as dummy
  from mytable
  order by `Group`, Age desc
) as x where x.row_number <= 2;
)
UNION ALL
(
select person, `group`, age
from 
(
   select person, `group`, age,
      @num := if(@group = `group`, @num + 1, 1) as row_number,
      @group := `group` as dummy
  from mytable
  order by `Group`, Age desc
) as x where x.row_number <= 2;
)

SQL FIDDLE

(UNIONed 查询只是用于测试目的的原始查询的副本)

Answer 1

你有一些额外的括号。

查看此 SQL Fiddle