—表连接Join–

—查询所有学生的姓名、年龄及所在班级

—使用子查询

select StudentName,DATEDIFF(yyyy,borndate,getdate()),(select classname from grade where ClassId=Student.ClassId) from Student

—使用from多表

select StudentName,DATEDIFF(yyyy,borndate,getdate()),classname

from Student,grade

where Student.ClassId=grade.ClassId

—使用多表连接  表 inner join 另外的表  on 如何建立关联(能够建立关联的字段一般就是能够创建主外键关系的字段)

select StudentName,DATEDIFF(yyyy,borndate,getdate()),classname

from Student

join grade on Student.ClassId=grade.ClassId

–1.内连接：inner join.找到两个表建立关系的字段值相等的记录,如果字段值不相等,那么就抛弃

—查询学生姓名、年龄、班级及成绩

select Student.StudentName,DATEDIFF(YYYY,Student.BornDate,GETDATE()),grade.classname,Result.StudentResult

from Student

inner join grade on Student.ClassId=grade.ClassId

inner join Result on Student.StudentNo=Result.StudentNo

where student.ClassId=2

—查询每个学员需要参加的考试科目名称

select Student.StudentNo,Student.StudentName,Subject.SubjectName

from Student

inner join Result on Student.StudentNo=Result.StudentNo

inner join Subject on Result.SubjectId=Subject.SubjectId

select Student.StudentNo,Student.StudentName,Subject.SubjectName

from Student

inner join Subject on Student.ClassId=Subject.ClassId

select * from PhoneType

inner join PhoneNum on PhoneNum.pTypeId=PhoneType.ptId

—左,右连接

—左连接，可以得到左表的所有记录，只不过如果左表的字段的值在右表中找不到相应的关联记录，那么右表中的所有字段会以null值替代

select * from PhoneType   left join  PhoneNum on PhoneNum.pTypeId=PhoneType.ptId

—查询没有参加考试的学员信息

select * from Student

left join Result on Student.StudentNo=Result.StudentNo

where Result.StudentNo is null and Result.SubjectId is null

—右连接:

select * from PhoneType left join PhoneNum on PhoneNum.pTypeId=PhoneType.ptId

—交叉连接:

select * from Student

cross join grade

—做多表连接的建议:

–1.先确定字段都来自于那一些表,通过  表.字段  的方式进行确定

–2.查看这些表都有那一些关联（可以建立主外键关系的字段），如果没有关联，考虑是否需要使用中间其它表进行关联

–3.多表连接后可以得到一个虚拟的表，可以对这个表的所有字段添加where条件

—练习1：查询所有英语及格的学生姓名、年龄及成绩

select Student.StudentName,DATEDIFF(YYYY,Student.BornDate,GETDATE()),Result.StudentResult

from Student

inner join Result on Student.StudentNo=Result.StudentNo

inner join Subject on Result.SubjectId=Subject.SubjectId

where Subject.SubjectName=’office’ and Result.StudentResult>=60

—练习2：查询所有参加考试的(english分数不为null)学生姓名、年龄及成绩

—练习3：查询所有学生(参加和未参加考试)的学生姓名、年龄、成绩，如果没有参加考试显示缺考,如果小于60分显示不及格office

select Student.StudentName,DATEDIFF(yyyy,student.borndate,getdate()),

case

 when Result.StudentResult is null then ‘没有考试‘

 when Result.StudentResult>=60 then cast(Result.StudentResult AS CHAR(3))

 else ‘不及格‘  

end

from Student

left join Result on Student.StudentNo=Result.StudentNo

inner join Subject on Result.SubjectId=Subject.SubjectId

where Subject.SubjectName=’office’

—变量的种类—全局变量

go

insert into grade values(‘fdasfas’)

select * from Student

select @@IDENTITY —它得到的值不是指点上一条语句，而是最近的insert语句的值

go

select * from Student

select @@ROWCOUNT

delete from Student where StudentNo=12433

select @@ROWCOUNT

go

–@@ERROR 得到最近这一条语句的错误号

select * from stu —语法错误的错误号得不到

select @@ERROR —针对于增加删除和修改而言,如果有错误那么错误号一定大于0，如果没有错误那么就一定是0

update Student set LoginPwd=’ss’ where StudentNo=1

update Student set LoginPwd=’ss’ where StudentNo=1

select * from Student

go

select @@ERROR

—视图

—视图的本质就是一句sql语句–select.它表示一张表的部分数据或多张表的综合数据，其结构和数据是建立在对表的查询基础上

—视图的本质就是一张虚拟表：它的操作与操作表基本一致

—视图里面并没有真正存储数据，它存储的是sql语句，当执行视图获取数据的时候，本质就是执行视图中的sql语句去获取数据

select * from Student

select * from vw_getstudentResultInfo

—通过命令语句创建视图

—语法：

–go

–create view vw_自定义名称

–as

— select 命令

–go

—获取六期班学员信息

–1.可不可以写多条select查询？只能写一条

–2。视图里面只能写select，不能添加任何的update/delete/insert语句

if exists(select * from sysobjects where name=’vw_getStudentByClassId_6′)

drop view vw_getStudentByClassId_6

go

create view vw_getStudentByClassId_6

as

 select top 2 * from Student order by studentname

go

—对视图进行查询

select * from vw_getStudentByClassId_6 order by studentname

—对视图进行修改,可以对视图进行删除增加和修改操作，况且操作会直接影响物理表，所以一般不建立去做这些操作，因为视图的本质目的是为查询

update vw_getStudentByClassId_6 set classhour = 10, subjectname=’c#’, classname=’111′ where subjectid=2

delete from vw_getStudentByClassId_6 where Studentno=3

—视图的增加删除和修改操作只能针对于单个表，如果涉及了多个表的操作，那么将不成功

select * from vw_getstudentResultInfo

delete from vw_getstudentResultInfo where Studentno=6

update vw_getstudentResultInfo set studentresult=55 , subjectname=’c#’ where Studentno=6

–CREATE  PROC[EDURE]  

–procedure

—子查询—

—一个查询里面还包含着另外一个查询

—子查询做为条件—

–1.包含在()里面先执行的查询就是子查询语句,包含子查询的就称为父查询语句

–2.引入子查询时，在选择列表中只能指定一个表达式,就是意味着子查询做为条件(有关系运算符)的时候子查询永远不可能出现多列的情况

–3.子查询返回的值不止一个。当子查询跟随在 =、!=、<、<=、>、>= 之后，或子查询用作表达式时，这种情况是不允许的,就意味着如果子查询跟在关系运算符之后，必须保证子查询只返回了单个值,如果真的需要这么做就可以使用关键字 in/not in

—查询比林思年龄大的学员信息

–4.有子查询的sql语句返回的列只与父查询有关，子查询中的列仅仅是做为条件判断

–1.先查询出林思的年龄

select borndate from Student where StudentName=’林思‘

—返回一行多列值—-做为条件永远错误

select * from Student where BornDate<(select * from Student where StudentName=’林思‘)

—返回多行一列值

select * from Student where BornDate<(select borndate from Student)

—查询班级ID《=3的学员信息

select classid from grade where ClassId<=3

select StudentNo,StudentName from Student where ClassId not in(select classid from grade where ClassId<=3)

—子查询得到某列的值 —用得最少

—查询学员是10的学员office考试成绩和考试日期,显示学员姓名

select (select studentname from student where studentno=10),StudentResult,ExamDate from Result where StudentNo=10 and SubjectId=(select SubjectId from Subject where SubjectName=’office’)

–3.查询得到结果集，可以使用子查询返回一张虚拟表

—查询班级ID为1的所有学员的考试成绩

–1查询出班级ID为1的学员的学号

select studentno from Student where ClassId=1

—查询指定学号的学员的成绩

select * from Result where StudentNo in(select studentno from Student where ClassId=1)

—分页

select top 5 * from Student

select top 5 * from Student where StudentNo not in(select top 5 StudentNo from Student order by StudentNo)

–ROW_NUMBER 可以为查询出的每一行返回一个行号，行号类似于标识列，永远不会重复，同是它默认是连续的,这个函数可以为结果集添加一个新列

–over说明在那一个字段上进行排序，因为按不同字段排序结果集的显示是不一样的

select ROW_NUMBER() over(order by studentno) as id,* from Student

—如果子查询做为结果集那么必须为其添加别名

select * from (select ROW_NUMBER() over(order by studentno) as id,* from Student) as temp

where temp.id>=6 and id<=10

—使用Row_number() over(指定排序字段)实现分页,这个函数可以为结果集添加一个新列

select ROW_NUMBER() over(order by studentno) as id,* from Student

select * from (select ROW_NUMBER() over(order by studentno) as id,* from Student

) as temp where  id>0 and id<=5

—查询年龄比“廖杨”大的学员，显示这些学员的信息

select * from Student where BornDate<(select BornDate from Student where StudentName=’廖杨‘)

—查询二期班开设的课程

select * from Subject where ClassId=(select ClassId from grade where classname=’二期班‘)

—查询参加最近一次“office”考试成绩最高分和最低分

select subjectid from Subject where SubjectName=’office’

select MAX(ExamDate) from Result where SubjectId=(select subjectid from Subject where SubjectName=’office’)

select  max(StudentResult),MIN(StudentResult) from Result where SubjectId=

(select subjectid from Subject where SubjectName=’office’)

and ExamDate=

(select MAX(ExamDate) from Result where SubjectId=

(select subjectid from Subject where SubjectName=’office’))

select * from Result

select * from Subject

—子查询的分类:

–1.独立子查询:单独可以运行的子查询

–2.相关子查询：子查询中引用了父查询中的列

—查询参加了考试的学员信息

select distinct StudentNo from Result

select * from Student where StudentNo in(select distinct StudentNo from Result)

select * from Student where StudentNo=(select distinct StudentNo from Result where Result.StudentNo=Student.StudentNo)

select StudentNo from Result where StudentNo=33

select * from Student where StudentNo=(select StudentNo from Result where StudentNo=33)