本篇文章主要介绍了"SQL Server T-SQL高级查询"，主要涉及到方面的内容，对于其他数据库感兴趣的同学可以参考一下：
高级查询在数据库中用得是最频繁的，也是应用最广泛的。? 基本常用查询--selectselect * from student; --all 查询所有selec...
高级查询在数据库中用得是最频繁的，也是应用最广泛的。
? 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;
? 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
);
? 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
select age from student
where age > 20 order by age compute sum(age) by age;
对年龄大于的按照性别进行分组汇总年龄信息
select id, sex, age from student
where age > 20 order by sex, age compute sum(age) by sex;
按照年龄分组汇总
select age from student
where age > 20 order by age, id compute sum(age);
按照年龄分组，年龄汇总，id找最大值
select id, age from student
where age > 20 order by age compute sum(age), max(id);
compute进行汇总前面是查询的结果，后面一条结果集就是汇总的信息。compute子句中可以添加多个汇总表达式，可以添加的信息如下：
a、 可选by关键字。它是每一列计算指定的行聚合
b、 行聚合函数名称。包括sum、avg、min、max、count等
c、 要对其执行聚合函数的列
compute by适合做先分组后汇总的业务。compute by后面的列一定要是order by中出现的列。
3、 cube汇总
cube汇总和compute效果类似，但语法较简洁，而且返回的是一个结果集。
