mysql 的常用查询 / 憋错料

? 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。

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

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

--减集（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

--简化联接查询

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

--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

--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

--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）

--自连接

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());--当前月份

select datePart(weekday, getDate());--当前星期

select datePart(second, getDate());--当前秒数

select day(getDate());--返回当前日期天数

select day(‘2011-06-30‘);--返回当前日期天数

select month(getDate());--返回当前日期月份

select month(‘2011-11-10‘);

select year(getDate());--返回当前日期年份

select year(‘2010-11-10‘);

select getDate();--当前系统日期

select getUTCDate();--utc日期

3、数学函数

select pi();--PI函数

select rand(100), rand(50), rand(), rand();--随机数

select round(rand(), 3), round(rand(100), 5);--精确小数位

--精确位数，负数表示小数点前

select round(123.456, 2), round(254.124, -2);

select round(123.4567, 1, 2);

4、元数据

select col_name(object_id(‘student‘), 1);--返回列名

select col_name(object_id(‘student‘), 2);

--该列数据类型长度

select col_length(‘student‘, col_name(object_id(‘student‘), 2));

--该列数据类型长度

select col_length(‘student‘, col_name(object_id(‘student‘), 1));

--返回类型名称、类型id

select type_name(type_id(‘varchar‘)), type_id(‘varchar‘);

--返回列类型长度

select columnProperty(object_id(‘student‘), ‘name‘, ‘PRECISION‘);

--返回列所在索引位置

select columnProperty(object_id(‘student‘), ‘sex‘, ‘ColumnId‘);

5、字符串函数

select ascii(‘a‘);--字符转换ascii值

select ascii(‘A‘);

select char(97);--ascii值转换字符

select char(65);

select nchar(65);

select nchar(45231);

select nchar(32993);--unicode转换字符

select unicode(‘A‘), unicode(‘中‘);--返回unicode编码值

select soundex(‘hello‘), soundex(‘world‘), soundex(‘word‘);

select patindex(‘%a‘, ‘ta‘), patindex(‘%ac%‘, ‘jack‘), patindex(‘dex%‘, ‘dexjack‘);--匹配字符索引

select ‘a‘ + space(2) + ‘b‘, ‘c‘ + space(5) + ‘d‘;--输出空格

select charIndex(‘o‘, ‘hello world‘);--查找索引

select charIndex(‘o‘, ‘hello world‘, 6);--查找索引

select quoteName(‘abc[]def‘), quoteName(‘123]45‘);

--精确数字

select str(123.456, 2), str(123.456, 3), str(123.456, 4);

select str(123.456, 9, 2), str(123.456, 9, 3), str(123.456, 6, 1), str(123.456, 9, 6);

select difference(‘hello‘, ‘helloWorld‘);--比较字符串相同

select difference(‘hello‘, ‘world‘);

select difference(‘hello‘, ‘llo‘);

select difference(‘hello‘, ‘hel‘);

select difference(‘hello‘, ‘hello‘);

select replace(‘abcedef‘, ‘e‘, ‘E‘);--替换字符串

select stuff(‘hello world‘, 3, 4, ‘ABC‘);--指定位置替换字符串

select replicate(‘abc#‘, 3);--重复字符串

select subString(‘abc‘, 1, 1), subString(‘abc‘, 1, 2), subString(‘hello Wrold‘, 7, 5);--截取字符串

select len(‘abc‘);--返回长度

select reverse(‘sqlServer‘);--反转字符串

select left(‘leftString‘, 4);--取左边字符串

select left(‘leftString‘, 7);

select right(‘leftString‘, 6);--取右边字符串

select right(‘leftString‘, 3);

select lower(‘aBc‘), lower(‘ABC‘);--小写

select upper(‘aBc‘), upper(‘abc‘);--大写

--去掉左边空格

select ltrim(‘ abc‘), ltrim(‘# abc#‘), ltrim(‘  abc‘);

--去掉右边空格

select rtrim(‘ abc    ‘), rtrim(‘# abc#   ‘), rtrim(‘abc‘);

6、安全函数

select current_user;

select user;

select user_id(), user_id(‘dbo‘), user_id(‘public‘), user_id(‘guest‘);

select user_name(), user_name(1), user_name(0), user_name(2);

select session_user;

select suser_id(‘sa‘);

select suser_sid(), suser_sid(‘sa‘), suser_sid(‘sysadmin‘), suser_sid(‘serveradmin‘);

select is_member(‘dbo‘), is_member(‘public‘);

select suser_name(), suser_name(1), suser_name(2), suser_name(3);

select suser_sname(), suser_sname(0x01), suser_sname(0x02), suser_sname(0x03);

select is_srvRoleMember(‘sysadmin‘), is_srvRoleMember(‘serveradmin‘);

select permissions(object_id(‘student‘));

select system_user;

select schema_id(), schema_id(‘dbo‘), schema_id(‘guest‘);

select schema_name(), schema_name(1), schema_name(2), schema_name(3);

7、系统函数

select app_name();--当前会话的应用程序名称

select cast(2011 as datetime), cast(‘10‘ as money), cast(‘0‘ as varbinary);--类型转换

select convert(datetime, ‘2011‘);--类型转换

select coalesce(null, ‘a‘), coalesce(‘123‘, ‘a‘);--返回其参数中第一个非空表达式

select collationProperty(‘Traditional_Spanish_CS_AS_KS_WS‘, ‘CodePage‘);

select current_timestamp;--当前时间戳

select current_user;

select isDate(getDate()), isDate(‘abc‘), isNumeric(1), isNumeric(‘a‘);

select dataLength(‘abc‘);

select host_id();

select host_name();

select db_name();

select ident_current(‘student‘), ident_current(‘classes‘);--返回主键id的最大值

select ident_incr(‘student‘), ident_incr(‘classes‘);--id的增量值

select ident_seed(‘student‘), ident_seed(‘classes‘);

select @@identity;--最后一次自增的值

select identity(int, 1, 1) as id into tab from student;--将studeng表的烈属，以/1自增形式创建一个tab

select * from tab;

select @@rowcount;--影响行数

select @@cursor_rows;--返回连接上打开的游标的当前限定行的数目

select @@error;--T-SQL的错误号

select @@procid;

8、配置函数

set datefirst 7;--设置每周的第一天，表示周日

select @@datefirst as ‘星期的第一天‘, datepart(dw, getDate()) AS ‘今天是星期‘;

select @@dbts;--返回当前数据库唯一时间戳

set language ‘Italian‘;

select @@langId as ‘Language ID‘;--返回语言id

select @@language as ‘Language Name‘;--返回当前语言名称

select @@lock_timeout;--返回当前会话的当前锁定超时设置（毫秒）

select @@max_connections;--返回SQL Server 实例允许同时进行的最大用户连接数

select @@MAX_PRECISION AS ‘Max Precision‘;--返回decimal 和numeric 数据类型所用的精度级别

select @@SERVERNAME;--SQL Server 的本地服务器的名称

select @@SERVICENAME;--服务名

select @@SPID;--当前会话进程id

select @@textSize;

select @@version;--当前数据库版本信息

9、系统统计函数

select @@CONNECTIONS;--连接数

select @@PACK_RECEIVED;

select @@CPU_BUSY;

select @@PACK_SENT;

select @@TIMETICKS;

select @@IDLE;

select @@TOTAL_ERRORS;

select @@IO_BUSY;

select @@TOTAL_READ;--读取磁盘次数

select @@PACKET_ERRORS;--发生的网络数据包错误数

select @@TOTAL_WRITE;--sqlserver执行的磁盘写入次数

select patIndex(‘%soft%‘, ‘microsoft SqlServer‘);

select patIndex(‘soft%‘, ‘software SqlServer‘);

select patIndex(‘%soft‘, ‘SqlServer microsoft‘);

select patIndex(‘%so_gr%‘, ‘Jsonisprogram‘);

10、用户自定义函数

# 查看当前数据库所有函数

--查询所有已创建函数

select definition,* from sys.sql_modules m join sys.objects o on m.object_id = o.object_id

and type in(‘fn‘, ‘if‘, ‘tf‘);

# 创建函数

if (object_id(‘fun_add‘, ‘fn‘) is not null)

    drop function fun_add

go

create function fun_add(@num1 int, @num2 int)

    returns int

with execute as caller

as

    begin

        declare @result int;

        if (@num1 is null)

            set @num1 = 0;

        if (@num2 is null)

            set @num2 = 0;

        set @result = @num1 + @num2;

        return @result;

end

go

调用函数

select dbo.fun_add(id, age) from student;

--自定义函数，字符串连接

if (object_id(‘fun_append‘, ‘fn‘) is not null)

    drop function fun_append

go

create function fun_append(@args nvarchar(1024), @args2 nvarchar(1024))

    returns nvarchar(2048)

as

    begin

        return @args + @args2;

end

go

select dbo.fun_append(name, ‘abc‘) from student;

# 修改函数

alter function fun_append(@args nvarchar(1024), @args2 nvarchar(1024))

    returns nvarchar(1024)

as

    begin

        declare @result varchar(1024);

        --coalesce返回第一个不为null的值

        set @args = coalesce(@args, ‘‘);

        set @args2 = coalesce(@args2, ‘‘);;

        set @result = @args + @args2;

        return @result;

end

go

select dbo.fun_append(name, ‘#abc‘) from student;

# 返回table类型函数

--返回table对象函数

select name, object_id, type from sys.objects where type in (‘fn‘, ‘if‘, ‘tf‘) or type like ‘%f%‘;

if (exists (select * from sys.objects where type in (‘fn‘, ‘if‘, ‘tf‘) and name = ‘fun_find_stuRecord‘))

    drop function fun_find_stuRecord

go

create function fun_find_stuRecord(@id int)

    returns table

as

    return (select * from student where id = @id);

go

select * from dbo.fun_find_stuRecord(2);