Question

我有一个工作查询，我需要重复几次，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（获取语法错误）：

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重复）

Answer 1

你有一些额外的括号。

请参阅此SQL Fiddle

Answer 2

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;

Answer 3

删除最外面的括号。 SELECT语句应该以SELECT关键字开头，而不是一个开放的paren。

不能UNION ALL两个等价的查询？

3 个答案: