您现在的位置是:网站首页> 编程资料编程资料

SQL Server 的T-SQL高级查询详解_MsSql_

2023-05-26 527人已围观

简介 SQL Server 的T-SQL高级查询详解_MsSql_

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

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。

select count(*), sex from student group by sex with cube; select count(*), age, sum(age) from student where age is not null group by age with cube;

cube要结合group by语句完成分组汇总

排序函数

排序在很多地方需要用到,需要对查询结果进行排序并且给出序号。比如:

1、 对某张表进行排序,序号需要递增不重复的

2、 对学生的成绩进行排序,得出名次,名次可以并列,但名次的序号是连续递增的

3、 在某些排序的情况下,需要跳空序号,虽然是并列

基本语法

排序函数 over([分组语句] 排序子句[desc][asc]) 排序子句 order by 列名, 列名 分组子句 partition by 分组列, 分组列

row_number函数

根据排序子句给出递增连续序号

按照名称排序的顺序递增 select s.id, s.name, cid, c.name, row_number() over(order by c.name) as number from student s, classes c where cid = c.id;

rank函数函数

根据排序子句给出递增的序号,但是存在并列并且跳空

select id, name, rank() over(order by cid) as rank from student; 跳过相同递增 select s.id, s.name, cid, c.name, rank() over(order by c.name) as rank from student s, classes c where cid = c.id;

dense_rank函数

根据排序子句给出递增的序号,但是存在并列不跳空

不跳过,直接递增 
                
                

-六神源码网