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SQL语句大全教程

时间：2021-07-01 10:21:17 帮助过：2人阅读

CREATE DATABASE DBNAME

删除数据库

DROP DATABASE DBNAME

Ø 基本常用查询

--select
select * from student;

--all 查询所有
select all sex from student;

--distinct 过滤重复

select distinct sex from student;

--count 统计

select count(*) from student;
select count(sex) from student;
select count(distinct sex) from student;

--top 取前N条记录

select top 3 * from student;

--alias column name 列重命名

select id as 编号, name ‘名称‘, sex 性别 from student;

--alias table name 表重命名

select id, name, s.id, s.name from student s;

--column 列运算

select (age + id) col from student;
select s.name + ‘-‘ + c.name from classes c, student s where s.cid = c.id;

--where 条件

select * from student where id = 2;
select * from student where id > 7;
select * from student where id < 3;
select * from student where id <> 3;
select * from student where id >= 3;
select * from student where id <= 5;
select * from student where id !> 3;
select * from student where id !< 5;

--and 并且

select * from student where id > 2 and sex = 1;

--or 或者

select * from student where id = 2 or sex = 1;

--between ... and ... 相当于并且
select * from student where id between 2 and 5;
select * from student where id not between 2 and 5;

--like 模糊查询

select * from student where name like ‘%a%‘;
select * from student where name like ‘%[a][o]%‘;
select * from student where name not like ‘%a%‘;
select * from student where name like ‘ja%‘;
select * from student where name not like ‘%[j,n]%‘;
select * from student where name like ‘%[j,n,a]%‘;
select * from student where name like ‘%[^ja,as,on]%‘;
select * from student where name like ‘%[ja_on]%‘;

--in 子查询

select * from student where id in (1, 2);

--not in 不在其中

select * from student where id not in (1, 2);

--is null 是空

select * from student where age is null;

--is not null 不为空

select * from student where age is not null;

--order by 排序

select * from student order by name;
select * from student order by name desc;
select * from student order by name asc;

--group by 分组

按照年龄进行分组统计
select count(age), age from student group by age;
按照性别进行分组统计
select count(*), sex from student group by sex;
按照年龄和性别组合分组统计，并排序
select count(*), sex from student group by sex, age order by age;
按照性别分组，并且是id大于2的记录最后按照性别排序
select count(*), sex from student where id > 2 group by sex order by sex;
查询id大于2的数据，并完成运算后的结果进行分组和排序
select count(*), (sex * id) new from student where id > 2 group by sex * id order by sex * id;

--group by all 所有分组

按照年龄分组，是所有的年龄
select count(*), age from student group by all age;

--having 分组过滤条件

按照年龄分组，过滤年龄为空的数据，并且统计分组的条数和现实年龄信息
select count(*), age from student group by age having age is not null;

按照年龄和cid组合分组，过滤条件是cid大于1的记录
select count(*), cid, sex from student group by cid, sex having cid > 1;

按照年龄分组，过滤条件是分组后的记录条数大于等于2
select count(*), age from student group by age having count(age) >= 2;

按照cid和性别组合分组，过滤条件是cid大于1，cid的最大值大于2
select count(*), cid, sex from student group by cid, sex having cid > 1 and max(cid) > 2;

Ø 嵌套子查询

子查询是一个嵌套在select、insert、update或delete语句或其他子查询中的查询。任何允许使用表达式的地方都可以使用子查询。子查询也称为内部查询或内部选择，而包含子查询的语句也成为外部查询或外部选择。

# from (select … table)示例
将一个table的查询结果当做一个新表进行查询
select * from (
select id, name from student where sex = 1
) t where t.id > 2;
上面括号中的语句，就是子查询语句（内部查询）。在外面的是外部查询，其中外部查询可以包含以下语句：
   1、包含常规选择列表组件的常规select查询
   2、包含一个或多个表或视图名称的常规from语句
   3、可选的where子句
   4、可选的group by子句
   5、可选的having子句

# 示例

查询班级信息，统计班级学生人生
select *, (select count(*) from student where cid = classes.id) as num
from classes order by num;

# in, not in子句查询示例

查询班级id大于小于的这些班级的学生信息
select * from student where cid in (
select id from classes where id > 2 and id < 4
);

查询不是班的学生信息
select * from student where cid not in (
select id from classes where name = ‘2班‘
)
in、not in 后面的子句返回的结果必须是一列，这一列的结果将会作为查询条件对应前面的条件。如cid对应子句的id；

# exists和not exists子句查询示例

查询存在班级id为的学生信息
select * from student where exists (
select * from classes where id = student.cid and id = 3
);

查询没有分配班级的学生信息
select * from student where not exists (
select * from classes where id = student.cid
);
exists和not exists查询需要内部查询和外部查询进行一个关联的条件，如果没有这个条件将是查询到的所有信息。如：id等于student.id；

# some、any、all子句查询示例

查询班级的学生年龄大于班级的学生的年龄的信息
select * from student where cid = 5 and age > all (
select age from student where cid = 3
);

select * from student where cid = 5 and age > any (
select age from student where cid = 3
);

select * from student where cid = 5 and age > some (
select age from student where cid = 3
);

Ø 聚合查询

1、 distinct去掉重复数据
select distinct sex from student;
select count(sex), count(distinct sex) from student;

2、 compute和compute by汇总查询

对年龄大于的进行汇总

SQL语句大全教程

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