sqlserver:分组随机取记录后，newID和union的冲突解决
刚才在CSDN回答了一个问题，数据库抽取30个单选题，10个多选，10个判断
想都没有想就敲下了语句：
select
top
30
*
from
test
where
typename
=
'
单选
'
order
by
newid
()
union
all
select
top
10
*
from
test
where
typename
=
'
多选
'
order
by
newid
()
union
all
select
top
10
*
from
test
where
typename
=
'
判断
'
order
by
newid
()
后来楼主说报错：
服务器: 消息 156，级别 15，状态 1，行 2
在关键字 'union' 附近有语法错误。
服务器: 消息 156，级别 15，状态 1，行 4
在关键字 'union' 附近有语法错误。
后来想了想，应该用 derived table
SELECT
*
FROM
(
select
top
30
*
from
exam_test
where
testtype
=
0
order
by
newid
())
as
a
UNION
ALL
SELECT
*
FROM
(
select
top
10
*
from
exam_test
where
testtype
=
1
order
by
newid
())
as
b
UNION
ALL
SELECT
*
FROM
(
select
top
10
*
from
exam_test
where
testtype
=
2
order
by
newid
())
as
c
这次应该可以了吧，而且在网上查了一下，看样子应该是可以了，谁知楼主又说报错：
如果语句中包含 UNION 运算符，那么 ORDER BY 子句中的项就必须出现在选择列表中。
真是郁闷啊，想不通为什么不行？有人告诉我答案吗？望知道的人不吝赐教（：
为了解决问题，只得在每个分组查询加一列，newid()，这相当不舒服。
SELECT
*
FROM
(
select
top
30
*
,
NewID
=
NEWID
()
from
exam_test
where
testtype
=
0
order
by
newid
())
as
a
UNION
ALL
SELECT
*
FROM
(
select
top
10
*
,
NewID
=
NEWID
()
from
exam_test
where
testtype
=
1
order
by
newid
())
as
b
UNION
ALL
SELECT
*
FROM
(
select
top
10
*
,
NewID
=
NEWID
()
from
exam_test
where
testtype
=
2
order
by
newid
())
as
c
不知道这样可不可以？应该是不行的，没有测试环境，sorry.
select * from
(select
top
30
*
from
test
where
typename
=
'
单选
'
union
all
select
top
10
*
from
test
where
typename
=
'
多选
'
union
all
select
top
10
*
from
test
where
typename
=
'
判断
'
) as a
order by newid()