case--end 和子查询

MSSQL操作 case end 和子查询 代码如下：

  1 create database Test

  2 go

  3 use Test

  4 go

  5 create table [user]

  6 (

  7     uId int identity(1,1) primary key,

  8     name varchar(50),

  9     level int  --1骨灰 2大虾 3菜鸟

 10 )

 11 go

 12 insert into [user] (name,level) values('犀利哥',1)

 13 insert into [user] (name,level) values('小月月',2)

 14 insert into [user] (name,level) values('芙蓉姐姐',3)

 15 

 16 select * from [user]

 17 

 18 --1、case end 相当于c#中的swith

 19 select [name],

 20     case [level] 

 21         when 1 then '骨灰' 

 22         when 2 then '大虾'

 23         when 3 then '菜鸟'

 24         else '神仙'

 25     end as '等级'

 26 from [user]

 27 

 28 --2、case end 相当于c#的多重if语句

 29 --注意：case end的返回值类型要一致

 30 use MySchool

 31 

 32 select * from score

 33 

 34 select studentId,

 35     case

 36         when english >=90 and english <=100 then 'A'

 37         when english between 80 and 89 then 'B'

 38         when english between 70 and 79 then 'C'

 39         when english between 60 and 69 then 'D'

 40         else 'E'

 41     end

 42 from score

 43 

 44 --练习1

 45 select 

 46     case 

 47         when a>b then a

 48         else b

 49     end,

 50     case 

 51         when b > c then b

 52         else c

 53     end

 54 from biao

 55 

 56 

 57 select abs(-39)

 58 

 59 --练习2

 60 use Test

 61 go

 62 create table test

 63 (

 64     number varchar(10),

 65     amount int

 66 )

 67 insert into test(number,amount) values('RK1',10)

 68 insert into test(number,amount) values('RK2',20)

 69 insert into test(number,amount) values('RK3',-30)

 70 insert into test(number,amount) values('RK4',-10)

 71 go

 72 

 73 select * from test

 74 

 75 select number,

 76     case

 77         when amount > 0 then amount

 78         else 0

 79     end as 收入,

 80     case 

 81         when amount < 0 then abs(amount)

 82         else 0

 83     end as 支出

 84 from test

 85 

 86 --增加练习

 87 name sex -- 0 1 

 88 select name,

 89     case sex

 90         when 1 then '男'

 91         when 0 then '女'

 92     end 

 93 from student

 94 --练习3

 95 use Test

 96 go

 97 CREATE TABLE student0 (name nvarchar(10),subject nvarchar(10),result int)

 98 INSERT INTO student0 VALUES ('张三','语文',80)

 99 INSERT INTO student0 VALUES ('张三','数学',90)

100 INSERT INTO student0 VALUES ('张三','物理',85)

101 INSERT INTO student0 VALUES ('李四','语文',85)

102 INSERT INTO student0 VALUES ('李四','数学',92)

103 INSERT INTO student0 VALUES ('李四','物理',null)

104 

105 SELECT * FROM student0

106 

107 select name,

108     sum(case subject

109         when '语文' then result

110     end) as '语文',

111     sum(case subject 

112         when '数学' then result

113     end) as '数学',

114     isnull(sum(case subject

115         when '物理' then result

116     end),0) as '物理'

117 from student0

118 group by name

119 

120 --isnull(,)

121 

122 

123 

124 use MySchool

125 select * from student

126 

127 select * from [user]

128 delete from [user] where uid in (7,8,9)

129 insert into [user] (uUserName,uPwd,uTimes) values('123','123',0)

130 select * from [user]

131 

132 

133 

134 --子查询

135 select * from (select * from student where sAge<23) as t

136 

137 --

138 select max(english) from score

139 union all

140 select min(english) from score

141 union all

142 select avg(english) from score

143 

144 select (select max(english) from score) as t,

145 (select min(english) from score),

146 (select avg(english) from score)

147 

148 --查询高二一班所有的学生

149 select * from class

150 select * from student

151 

152 --当=、!=、<、<=、>、>=号后面是子查询的时候，

153 --子查询必须返回一列

154 --子查询必须返回一行

155 --错误的情况，因为子查询返回多行

156 select * from student where sClassId=

157 (select cId from class where cName='高二一班' or cName='高二二班')

158 

159 

160 --查询所有高二的学生

161 select * from student where sClassId in 

162 (select cId from class where cName like '高二%')

163 

164 --查询刘关张 的成绩

165 select * from score where studentId in

166 (select sId from student where sName in ('曹操','夏侯惇','张飞'))

167 

168 --子查询删除数据

169 delete from score where studentId in 

170 (select sId from student where sName in ('曹操','夏侯惇') )

171 

172 select * from score

173 

174 --分页

175 

176 select top 5 * from student order by sId desc

177 --查询最近插入的第6-10个人。除了前5个人的前5条

178 select top 5 * from student where sId not in

179 (select top (5*(3-1)) sId from student order by sId desc)

180 order by sId desc

181 

182 --sql 2005以后生成连续的编号

183 insert into student (sName,sSex,sAge) values('abc','男',18)

184 

185 select row_number() over(order by sId desc),*

186 from student

187 

188 select * from 

189 (select *,row_number() over(order by sId desc) as [no] from student) as t

190 where t.[no] between (5*(3-1))+1 and (5*3)

191 order by sId desc

192 

193 

194 select * from student