SQL Server T-SQL高级查询

Posted 2020-08-06 gyt_ing

转自：http://www.cnblogs.com/hoojo/archive/2011/07/16/2108129.html

 

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;
 
--按照性别和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2小于4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2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3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20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

根据排序子句给出递增的序号，但是存在并列并且跳空

顺序递增

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

select s.id, s.name, cid, c.name, dense_rank() over(order by c.name) as dense 
from student s, classes c where cid = c.id;

 

 

# partition by分组子句

可以完成对分组的数据进行增加排序，partition by可以与以上三个函数联合使用。

利用partition by按照班级名称分组，学生id排序

select s.id, s.name, cid, c.name, row_number() over(partition by c.name order by s.id) as rank 
from student s, classes c where cid = c.id;
 
select s.id, s.name, cid, c.name, rank() over(partition by c.name order by s.id) as rank 
from student s, classes c where cid = c.id;
 
select s.id, s.name, cid, c.name, dense_rank() over(partition by c.name order by s.id) as rank 
from student s, classes c where cid = c.id;

 

 

# ntile平均排序函数

将要排序的数据进行平分，然后按照等分排序。ntile中的参数代表分成多少等分。

select s.id, s.name, cid, c.name, 
ntile(5) over(order by c.name) as ntile 
from student s, classes c where cid = c.id;

 

 

• 集合运算

操作两组查询结果，进行交集、并集、减集运算

1、 union和union all进行并集运算

union 并集、不重复

select id, name from student where name like \'ja%\'
union
select id, name from student where id = 4;

并集、重复

select * from student where name like \'ja%\'
union all
select * from student;

2、 intersect进行交集运算

交集（相同部分）

select * from student where name like \'ja%\'
intersect
select * from student;

3、 except进行减集运算

交集（除相同部分）

select * from student where name like \'ja%\'
except
select * from student where name like \'jas%\';

 

 

• 公式表表达式

查询表的时候，有时候中间表需要重复使用，这些子查询被重复查询调用，不但效率低，而且可读性低，不利于理解。那么公式表表达式可以解决这个问题。

我们可以将公式表表达式（CET）视为临时结果集，在select、insert、update、delete或是create view语句的执行范围内进行定义。

表达式

with statNum(id, num) as 
(
    select cid, count(*) 
    from student 
    where id > 0
    group by cid
)
select id, num from statNum order by id;
 
with statNum(id, num) as 
(
    select cid, count(*) 
    from student 
    where id > 0
    group by cid
)
select max(id), avg(num) from statNum;

 

 

• 连接查询

1、 简化连接查询

select s.id, s.name, c.id, c.name
from student s, classes c
where s.cid = c.id;

2、 left join左连接

select s.id, s.name, c.id, c.name
from student s
left join classes c on s.cid = c.id;

3、 right join右连接

select s.id, s.name, c.id, c.name from student s right join classes c on s.cid = c.id;

4、 inner join内连接

select s.id, s.name, c.id, c.name from student s inner join classes c on s.cid = c.id;

inner可以省略

select s.id, s.name, c.id, c.name from student s join classes c on s.cid = c.id;

5、 cross join交叉连接

交叉联接查询，结果是一个笛卡儿乘积

select s.id, s.name, c.id, c.name from student s cross join classes c
--where s.cid = c.id;

6、 自连接（同一张表进行连接查询）

select distinct s.* from student s, student s1 where s.id <> s1.id and s.sex = s1.sex;

 

 

• 函数

1、 聚合函数

max最大值、min最小值、count统计、avg平均值、sum求和、var求方差

select 
    max(age) max_age, 
    min(age) min_age, 
    count(age) count_age, 
    avg(age) avg_age, 
    sum(age) sum_age, 
    var(age) var_age 
from student;

2、 日期时间函数

select dateAdd(day, 3, getDate());--加天
select dateAdd(year, 3, getDate());--加年
select dateAdd(hour, 3, getDate());--加小时

返回跨两个指定日期的日期边界数和时间边界数

select dateDiff(day, \'2011-06-20\', getDate());

相差秒数

select dateDiff(second, \'2011-06-22 11:00:00\', getDate());

相差小时数

select dateDiff(hour, \'2011-06-22 10:00:00\', getDate());

select dateName(month, getDate());--当前月份
select dateName(minute, getDate());--当前分钟
select dateName(weekday, getDate());--当前星期
select datePart(month, getDate());2017-3-10 SQL server   T-sql语句   高级查询

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