MySQL常用SQL语句总结包含复杂SQL查询

时间:2022-05-27 20:22:56

1、复杂SQL查询

1.1、单表查询

(1)选择指定的列

[例]查询全体学生的学号和姓名

select Sno as 学号,Sname as 姓名 from student;
select Sno,Sname from student;

(2)查询全部列

[例]查询全体学生的详细信息

select * from student;

(3)对查询后的指定列进行命名

[例]查询全部学生的“姓名”及其“出生年”两列

select Sname as 姓名,(2014-Sage) as 出生年 from student;
select Sname ,(2014-Sage) from student;

(4)消除取值重复的行

[例]查询选修了课程的学生学号

select distinct Sno as 选修了课程的学生学号 from SC;
select distinct Sno from SC;

(5)选择表中若干元组(满足条件的)

1.2、大小比较

[例]查询计算机系(IS)全体学生名单

select Sname as 学生姓名 from student where Sdept='IS';

[例]查询全体20岁以下的学生姓名和年龄

select Sname as 姓名,Sage as 年龄 from student where Sage<20;

1.3、确定范围

[例]查询所有在20到23岁(含20和23)的学生姓名、系别和年龄

select Sname as 姓名,Sdept as 系别,Sage as 年龄 from student where Sage between20 and 23;

注意between 小数 and 大数。

1.4、in和not in确定集合

[例]查询IS系和CS系的全体学生姓名和性别

select Sname as 姓名,Ssex as 性别 from student where Sdept='IS' or Sdept='CS';
select Sname as 姓名,Ssex as 性别 from student where Sdept in ('IS','CS');

[例]查询既不属于IS系,也不属于MA系的学生姓名和年龄

select Sname as 姓名,Sage as 年龄 from student where Sdept !='IS'and Sdept!='CS';
select Sname as 姓名,Sage as 年龄 from student where Sdept not in('IS','MA');

1.5、字符匹配(like % _ )

[例]查询所有姓李的学生姓名和性别

select Sname as 姓名,Ssex as 性别 from student where Sname like '李%';

[例]查询所有“2002”年入学的学生学号、姓名和系别

select Sno as 学号,Sname as 姓名,Sdept as 系别 from student where Sno like'2002%';

[例]查询所有不姓“刘”的学生信息

select * from student where Sname not like'刘%';

[例]查询名称含有“数据”的课程号、课程名及学分

select Cno as 课程号,Cname as 课程名,Ccredit as 学分 from course where Cname like '%数据%';

总结:

select * from course where cname like '%数据%';包含数据的字符串 
select * from course where cname like '数据%';以数据开头的字符串
select * from course where cname like '%数据'; 以数据结尾的字符串

1.6、涉及空值的查询(is null)

[例]查询没有先修课的课程号和课程名

select Cno as 课程号,Cname as 课程名,Cpno from course where Cpno is null;

[例]查询所有有成绩的学生学号、课程号及成绩

select Sno as 学号,Cno as 课程号,Grade as 成绩 from SC where Grade is not null;

1.7、查询结果排序(order by )

[例]查询选修了3号课程的学生学号和成绩,结果按成绩降序排列。

select Sno as 学号,Grade as 成绩 from SC where Cno=3 order by Grade desc;

[例]查询选修了3号课程的学生学号和成绩,结果按成绩升序排列。

select Sno as 学号,Grade as 成绩 from SC where Cno=3 order by Grade asc;

1.8、聚集函数

count、sum、avg、max、min

[例]查询学生总数

select count(*) as 学生总数 from student;

[例]查询所有课程的总学分

select sum(Ccredit) as 所有课程总学分 from course;

[例]查询全体学生平均年龄

select avg(Sage) as 平均年龄 from student;

[例]查询1号课程的最高分

select max(Grade) as 1号课程的最高分 from SC where Cno=1;

1.9、分组统计(group by)

[例]查询男女学生各有多少人。

select Ssex as 性别,count(*) as 人数 from student group by Ssex;

[例]查询每个课程的课程号和平均分。

select Cno as 课程号,avg(Grade) as 平均分 from SC group by Cno;

【例】查询选修了3门课程以上(含3门)的学生学号和选修课程数。

select Sno as 学号 ,count(course.Cno) as 选修课程数
From SC,course
Where course.Cno=SC.Cno
Group by Sno
Having Count(course.Cno)>=3;

having 关键字后面直接跟聚集函数

在 SQL 中增加 HAVING 子句原因是,WHERE 关键字无法与合计函数一起使用。

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value

【例】查询选修了2门课程以上(含2门,但不含1号课程),学生学号和选修课程数。

select Sno as 学号 ,count(course.Cno) as 选修课程数
From SC,course
Where course.Cno=SC.Cno and course.Cno !=1
Group by Sno
Having Count(course.Cno)>=2;

【例】查询不及格门数2门以上的学生学号。

Select Sno
from sc
Where sc.Grade<60
Group by Sno
Having count(Cno)>=2;

【例】查询有2名以上(含2名)学生选修了的课程号和选修人数。

Select Cno,count(Sno)
From SC
Group by Cno
Having count(sno)>=2

2、连接查询

(1)等值与非等值连接查询

[例]查询每个学生及其的选修课程情况

select student.Sno as 学号,course.Cno as 选修课号,SC.Grade as 成绩 
from student,course,SC 
where student.Sno=SC.Sno and course.Cno=SC.Cno ;

(2)自身连接

[例]查询每个学生的间接选修课

select SC.Sno as 学号,
FIRST.Cname as 直接选修课,
SECOND.Cname as 间接选修课
from SC,
course as FIRST,
course as SECOND
where FIRST.Cno=SC.Cno
and FIRST.Cpno=SECOND.Cno;

(3)外连接

[例]查询所有学生选修课程情况(含没选修课程的学生)

select student.Sno as 学号,
Sname as 姓名,
sc.Cno as 选修课程号
from student 
LEFT OUTER JOIN SC ON student.Sno=SC.Sno;

join 用于根据两个或多个表中的列之间的关系,从这些表中查询数据

JOIN: 如果表中有至少一个匹配,则返回行
LEFT JOIN: 即使右表中没有匹配,也从左表返回所有的行
RIGHT JOIN: 即使左表中没有匹配,也从右表返回所有的行
FULL JOIN: 只要其中一个表中存在匹配,就返回行
UNION 操作符用于合并两个或多个 SELECT 语句的结果集。
请注意,UNION 内部的 SELECT 语句必须拥有相同数量的列。列也必须拥有相似的数据类型。同时,每条 SELECT 语句中的列的顺序必须相同。

3 、嵌套查询

(1)带有IN谓词的子查询( 属性 in (子查询的查询结果) )

【例】查询与王敏同学在同一个系的学生信息。

select *
from student
where Sdept in (
 select Sdept
 from student
 where Sname='王敏'
);

【例】查询不与王敏同学不在同一个系的学生信息。

select *
from student
where Sdept not in (
 select Sdept
 from student
 whereSname='王敏'
);

【例】查询选修了课程名是“信息系统”的学生学号和姓名。

select student.Sno as 学号, Sname as 姓名
from student,SC
where student.Sno=SC.Sno and Cno in (
 select Cno
 from course
 where Cname='信息系统'
)

【例】查询曾与刘晨一同上课的学生学号和姓名。(假设:一个课程只有一个上课班)

select distinct student.Sno as 学号, Sname as 姓名
from student,SC
where student.Sno=SC.Sno and Cno in (
 select Cno
 from SC,student
 where SC.Sno=student.Sno and student.Sno in (
 select Sno
 from student
 where student.Sname='刘晨'
 )
)
  • 内层in 查出刘晨的学号sno,外层in查出刘晨所上课程的课程号。

(2)带有比较运算符的子查询(=,>=,<=,<>或!=)

【例】查询与王敏同学在同一个系的所有学生信息  (=判断)

select *
from student
where Sdept=(
 select Sdept
 from student
 where Sname='王敏'
)

【例】查询每个学生超过该课程最低分的课程号。(同类课程不是最低分的),子查询的结果返回一个数的时候,这个子查询就可以当一个数用?可以使用in符号,或者大于小于符号。

select Cno
from SC a
where Grade> (
 select min(Grade)
 from SC b
 where a.Cno=b.Cno
)

【例】查询每个学生超过他选修课程平均成绩的课程号。

select Cno
from SC a
where Grade> (
 select avg(Grade)
 from SC b
 where a.Sno=b.Sno
)

(3)带有ANY或ALL谓词的子查询

  • ANY表示任何一个,ALL表示所有,可以用在子查询的括号前面

【例】查询其他系中比计算机系某一学生年龄小的学生姓名,性别、年龄和所在系。

select Sname as 姓名,Ssex as 性别, Sage as 年龄, Sdept as 所在系
from student
where Sage <(
 select Sage
 from student
 where Sdept='CS'
);

【例】查询其他系中比计算机系所有年龄都小的学生姓名和年龄。

select Sname as 姓名, Sage as 年龄
from student
where Sdept<>'CS' and Sage <ALL (
 select Sage
 from student
 where Sdept='CS'
);

(4 )带有Exists谓词的子查询

【例】查询所有选修了1号课程的学生姓名。

select Sname as 姓名
from student
where Exists (
 select *
 from SC
 where Cno=1 and Sno=Student.Sno
);

4、集合查询

(1)并UNION

【例】 查询计算机系的学生及年龄不大于19岁的学生详细信息。

select *
from student
where student.Sdept='CS'
union
select *
from student
where student.Sage<=19;

(2)交INTERSECT

【例】查询选修了1号课程的与年龄不大于19岁的 学生 详细信息 的交集。

Select *
from student,SC
where student.Sno=SC.Sno and SC.Cno=1
INTERSECT
Select *
from student
where student.Sage<=19;

(3)差EXCEPT

【例】查询计算机科学系的学生与年龄不大于19岁的学生详细信息的差集。

select *
from student
where student.Sdept='SC'
EXCEPT
select *
from student
where student.Sage<=19;

总结

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