简单查询：一、投影select * from 表名 select 列1,列2... from 表名 select distinct 列名 from 表名二、筛选select top 数字 列|* from 表名 （一）等值与不等值 select * from 表名 where 列名=值 select * from 表名 where 列名!=值 select * from 表名 where 列名>值 select * from 表名 where 列名<值 select * from 表名 where 列名>=值 select * from 表名 where 列名<=值（二）多条件与范围 select * from 表名 where 条件1 and|or 条件2 ... select * from 表名 where between ... and ... select * from 表名 where 列 in (值列表)（三）模糊查询 like % _ select * from 表名 where 列 like ‘%_....‘三、排序select * from 表名 where 条件 order by 列名 ASC|DESC,列名 ASC|DESC四、分组：统计函数（聚合函数） count(), max(), min(), sum(), avg()count()统计总行数 count(*)得到所有的行数 count(列)得到该列中所有非null个数。 select COUNT(*) from car where Brand=‘b003‘max(列) 这一列的最大，min(列)这一列的最小 select min(price) from carsum(列)这一列的和，avg(列)这一列的平均 select AVG(price) from cargroup by ...having...1.group by后面跟的是列名。 2.一旦使用group by分组了，则select和from中间就不能用*，只能包含两类东西一类是：group by 后面的列名，另一类是统计函数 select Oil,avg(price) from Car group by oil 对于统计函数生成的列，默认是无列名，可以通过下面的方法指定列名。 select Oil as 油耗,COUNT(*) as 数量,avg(price) 均价 from Car group by oilhaving后面一般跟得是统计函数。它用来对分组后的数据进一步筛选。复杂查询：一、连接查询把多个表的列合在一个界面视图中。 思想：1.生成笛卡尔积。2.对笛卡尔积进行筛选。3.选择列进行显示。 select 表1.列1,表1.列2,表2.列1,表2.列2…… from 表1,表2 where 表1.列=表2.列select * from 表1     join 表2 on 表1.列=表2.列     join 表3 on 表2.列=表3.列左连(left join)，右连(right join),全连(full join)二、联合查询把多个表的行合在一个界面视图中。 用union把两个查询组合在一起。要求是这两个查询的列要一一对应。三、子查询（嵌套查询）(一)无关子查询： 至少是两层查询，在外层查询的里面再写查询。 里层查询为外层查询提供查询的中间内容。(二)相关子查询：  范例：复制代码--1、 查询Student表中的所有记录的Sname、Ssex和Class列。select sname,ssex,class from student--2、 查询教师所有的单位即不重复的Depart列。select distinct depart from teacher--3、 查询Student表的所有记录。--4、 查询Score表中成绩在60到80之间的所有记录。select * from score where degree  between 60 and 80--5、 查询Score表中成绩为85，86或88的记录。select * from score where degree in(85,86,88)--6、 查询Student表中“95031”班或性别为“女”的同学记录。select * from student where class=‘95031‘ or ssex=‘女‘--7、 以Class降序查询Student表的所有记录。select * from student order by class desc--8、 以Cno升序、Degree降序查询Score表的所有记录。select * from score order by cno asc,degree desc--9、 查询“95031”班的学生人数。select COUNT(*) from student where class=‘95031‘--10、查询Score表中的最高分的学生学号和课程号。select * from scoreselect MAX(degree) from score   --92select sno,cno from score where degree=(select MAX(degree) from score)--11、查询‘3-105’号课程的平均分。select AVG(degree) from score where cno=‘3-105‘--12、查询Score表中至少有5名学生选修的并以3开头的课程的平均分数。select cno,AVG(degree) from score where cno like ‘3%‘ group by cno having count(*)>=5--13、查询最低分大于70，最高分小于90的Sno列。--假定按学生算。select sno,MAX(degree),MIN(degree) from score group by sno having MAX(degree)<90 and MIN(degree)>70--14、查询所有学生的Sname、Cno和Degree列。select * from studentselect * from scoreselect sname,cno,degree from student join score on student.sno = score.sno--15、查询所有学生的Sno、Cname和Degree列。select * from courseselect * from scoreselect sno,cname,degree from course join score on course.cno = score.cno--16、查询所有学生的Sname、Cname和Degree列。select * from studentselect * from courseselect * from scoreselect sname,cname,degree from student    join score on student.sno = score.sno    join course on course.cno = score.cno--17、查询“95033”班所选课程的平均分。select * from studentselect * from scoreselect sno from student where class=‘95033‘   --101,107,108select * from score where sno in(101,107,108)select AVG(degree) from score where sno in(select sno from student where class=‘95033‘ )select AVG(score.degree) from student join score on student.sno = score.sno where student.class=‘95033‘--18、假设使用如下命令建立了一个grade表：create table grade(low  int,upp  int,rank  varchar(1))insert into grade values(90,100,‘A‘)insert into grade values(80,89,‘B‘)insert into grade values(70,79,‘C‘)insert into grade values(60,69,‘D‘)insert into grade values(0,59,‘E‘)--现查询所有同学的Sno、Cno和rank列。select * from gradeselect * from scoreselect sno,cno,rank from grade join score on score.degree>=grade.low and score.degree<=grade.upp--19、查询选修“3-105”课程的成绩高于“109”号同学成绩的所有同学的记录。select * from scoreselect * from score where cno=‘3-105‘  and degree>(select degree from score where cno=‘3-105‘ and sno=‘109‘)select degree from score where cno=‘3-105‘ and sno=‘109‘   --76复制代码复制代码--21、查询成绩高于学号为“109”、课程号为“3-105”的成绩的所有记录。select *from score where degree >(select degree from score  where sno=‘109‘and cno=‘3-105‘)--22、查询和学号为108的同学同年出生的所有学生的Sno、Sname和Sbirthday列。select sno,sname,sbirthday from student where year (sbirthday)=(select year(sbirthday) from student where sno=‘108‘) --23、查询“张旭“教师任课的学生成绩。select *from score where cno=(select cno from course where tno=( select tno from teacher where tname=‘张旭‘))--24、查询选修某课程的同学人数多于5人的教师姓名。select tname from teacher where tno=( select tno from course where cno in( select cno from score  group by cno having count(*)>5))--25、查询95033班和95031班全体学生的记录。select * from score where sno in( select sno from student where class in(‘95033‘,‘95031‘))--26、查询存在有85分以上成绩的课程Cno.select distinct cno from score where degree >85--27、查询出“计算机系“教师所教课程的成绩表。select *from score where cno in( select cno from course where tno in(select tno from teacher where depart =‘计算机系‘)--28、查询“计算机系”与“电子工程系“不同职称的教师的Tname和Prof。select tname,prof  from teacher --29、查询选修编号为“3-105“课程且成绩至少高于选修编号为“3-245”的同学的Cno、Sno和Degree,并按Degree从高到低次序排序。select cno from score group by cno having select degree from   where cno =‘3-105‘and degree >(select degree from score where cno=‘3-105‘ and sno=‘3-245‘)