case 嵌套查询与连接查询你需要懂得

判断类似一个班级的男生和女生的人数,用sum (cese when then ) 复制代码 代码如下: select
count(er.execute_result), sum(case er.execute_result when 1 then 1
else 0 end) completed, sum(case er.execute_result when 0 then 1 else 0
end) notCompleted from taw_wp_execute_result er ; 复制代码 代码如下: select (case when
er.execute_result0 then ‘a’ else ‘b’ end ) from
taw_wp_execute_result er ;

因为要牵扯到小计,所以需要计算两次。

1、Case 子查询连接查询复制代码
代码如下:select * from score create database demo use demo create table
[user] ( [uId] int identity( 1 ,1 ) primary key, [name] varchar (
50), [level] int –1骨灰大虾菜鸟 ) insert into [user] ( name, level
) values (‘ 犀利哥 ‘, 1 ) insert into [user] ( name, level ) values (‘
小月月 ‘, 2 ) insert into [user] ( name, level ) values (‘ 芙蓉姐姐 ‘,
3 ) –case end 单值判断 相当于 switch case –then
后面的返回值类型必须一致 select [name] , case [level] when 1 then
‘骨灰 ‘ when 2 then ‘大虾 ‘ when 3 then ‘菜鸟 ‘ end as ‘等级 ‘ from
[user] use MySchool select * from score –case end
第二种用法,相当于多重 if 语句 select studentId , case when english =90
then ‘ 优 ‘ when english =80 and english 90 then ‘ 良 ‘ when english =70
and english 80 then ‘ 中 ‘ when english = 60 and english 70 then ‘ 可 ‘
else ‘ 差 ‘ end as ‘成绩 ‘ from score order by english — 表中有A B C
三列 ,用 SQL 语句实现:当 A列大于 B 列时选择A 列否则选择 B 列,当B
列大于 C列时选择 B 列否则选择 C列。 select case when a b then a else b
end , case when b c then b else c end from T — 练习 create table test (
number varchar ( 10), amount int ) insert into test( number ,amount )
values ( ‘RK1’, 10 ) insert into test( number ,amount ) values ( ‘RK2’,
20 ) insert into test( number ,amount ) values ( ‘RK3’,- 30 ) insert
into test( number ,amount ) values ( ‘RK4’,- 10 ) select number , case
when amount 0 then amount else 0 end as ‘收入 ‘ , case when amount 0
then abs ( amount) else 0 end as ‘支出 ‘ from test –结果如下复制代码 代码如下:– 有一张表student0
,记录学生成绩 use demo CREATE TABLE student0 ( name nvarchar (10 ),
subject nvarchar (10 ), result int ) INSERT INTO student0 VALUES (‘ 张三
‘, ‘ 语文’ , 80) INSERT INTO student0 VALUES (‘ 张三 ‘, ‘ 数学’ , 90)
INSERT INTO student0 VALUES (‘ 张三 ‘, ‘ 物理’ , 85) INSERT INTO
student0 VALUES (‘ 李四 ‘, ‘ 语文’ , 85) INSERT INTO student0 VALUES (‘
李四 ‘, ‘ 数学’ , 92) INSERT INTO student0 VALUES (‘ 李四 ‘, ‘ 物理’
,null) select * from student0 select [name] , isnull (sum ( case
subject when ‘ 语文 ‘ then result end ),0 ) as ‘语文 ‘ , isnull (sum (
case subject when ‘ 数学 ‘ then result end ),0 ) as ‘数学 ‘ , isnull
(sum ( case subject when ‘ 物理 ‘ then result end ),0 ) as ‘物理 ‘ from
student0 group by [name]复制代码
代码如下:– 子查询将一个查询语句做为一个结果集供其他 SQL
语句使用,就像使用普通的表一样, —
被当作结果集的查询语句被称为子查询。所有可以使用表的地方几乎都可以使用子查询来代替。
use myschool select sName from ( select * from student ) as t select
1,( select sum ( english) from score ) as ‘ 和 ‘,( select avg ( sAge)
from student ) as ‘ 平均年龄 ‘ — 查询高一一班所有的学生 select * from
student where sClassId = ( select cId from class where cName = ‘高一一班
‘ ) — 查询高一一班 高二一班所有的学生 —
子查询返回的值不止一个。当子查询跟随在 = 、!= 、 、 = 、 、 = 之后 —
子查询跟在比较运算符之后,要求子查询只返回一个值 —
如果子查询是多行单列的子查询,这样的子查询的结果集其实是一个集合。可以使用
in 关键字代替 =号 select * from student where sClassId = ( select cId
from class where cName in ( ‘高一一班 ‘ ,’ 高二一班 ‘)) select * from
student where sClassId in ( select cId from class where cName in (
‘高一一班 ‘ ,’ 高二一班 ‘)) — 查询刘关张的成绩 select *澳门金沙vip, from score
where studentId in ( select sId from student where sName in ( ‘刘备 ‘ ,’
关羽 ‘, ‘ 张飞’ )) — 删除刘关张 delete from score where studentId in (
select sId from student where sName in ( ‘刘备 ‘ ,’ 关羽 ‘, ‘ 张飞’ ))
— 实现分页 — 最近入学的个学生 select top 3 * from student order by
sId desc — 查询第到个学生 select top 3 * from student where sId not in
( select top 3 sId from student order by sId desc) order by sId desc —
查询到的学生 select top 3 * from student where sId not in ( select top
6 sId from student order by sId desc) order by sId desc — 上面是sql
2000 以前的实现方式。 SQLServer2005 后增加了Row_Number 函数简化实现。
–sql 2005 中的分页 select * from ( select row_number () over (order
by sId desc ) as num,* from student ) as t where num between 1 and 3
select * from ( select row_number () over (order by sId desc ) as
num,* from student ) as t where num between 4 and 6 select * from (
select row_number () over (order by sId desc ) as num,* from student )
as t where num between 7 and 9 select * from ( select row_number ()
over (order by sId desc ) as num,* from student ) as t where num
between 3 *( 3- 1 ) + 1 and 3 *3 — 表连接 — 交叉连接cross join
select * from student cross join class — 内连接inner join…on…
select * from student inner join class on sClassId = cId select * from
class — 查询所有学生的姓名、年龄及所在班级 select sName , sAge, cName
,sSex from student inner join class on sClassId = cId where sSex =’ 女 ‘
— 查询年龄超过岁的学生的姓名、年龄及所在班级 select sName , sAge, cName
from class inner join student on sClassId = cId where sAge 20 — 外连接
–left join…on… select sName , sAge, cName from class

想法:

1、把查询到的结果,插入到临时表,

2、把统计结果插入到临时表。

3、查询临时表记录放置到游标中。

4、删除临时表记录。

包的定义声明:

复制代码 代码如下: