MySQL 高级函数

Ø 基本常用查询

-- all 查询所有,几乎从来不用 all 关键字,因为是默认关键字
select all sex from student;
-- distinct 过滤重复 (常用语检查一列数据是否有异常值)
select distinct sex from student;
-- count 统计
select count(distinct sex) from student;
-- top 取前N条记录
select top 3 * from student;
-- 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;
-- 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。

-- 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

-- 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;
-- 查询班级id大于小于X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X班的学生信息
select * from student where cid not in (
    select id from classes where name = '2班')
-- all,any,some
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20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

Ø 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;
-- 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 
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。 
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;

Ø 集合运算

操作两组查询结果，进行交集、并集、减集运算

-- union 并集、不重复
select id, name from student where name like 'ja%'
union select id, name from student where id = 4;
-- union all 并集、重复
select * from student where name like 'ja%'
union all select * from student;
-- 交集（相同部分）
select * from student where name like 'ja%'
intersect select * from student;
-- 减集（除相同部分）
select * from student where name like 'ja%'
except select * from student where name like 'jas%';

Ø 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。

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;

Ø 表的联合查询

-- 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;
-- 左连接 (左为基表)
select s.id, s.name, c.id, c.name from student s left join classes c on s.cid = c.id;
-- 右连接 (右为基表)
select s.id, s.name, c.id, c.name from student s right join classes c on s.cid = c.id;
-- 内连接 (等值联合)
select s.id, s.name, c.id, c.name from student s inner join classes c on s.cid = c.id;
-- 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 ,classes c
-- 自连接
select distinct s.* from student s, student s1 where s.id <> s1.id and s.sex = s1.sex;

Ø 函数

聚合函数

-- 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;

时间日期函数

select dateAdd(day, 3, getDate());
select dateAdd(year, 3, getDate());
select dateAdd(hour, 3, getDate());
select dateDiff(day, '2011-06-20', getDate());
select dateDiff(second, '2011-06-22 11:00:00', getDate());
select dateDiff(hour, '2011-06-22 10:00:00', getDate());
select dateName(month, getDate());
select dateName(minute, getDate());
select dateName(weekday, getDate());
select datePart(month, getDate());
select datePart(weekday, getDate());
select datePart(second, getDate());
select day(getDate());
select day('2011-06-30');
select month(getDate());
select month('2011-11-10');
select year(getDate());
select year('2010-11-10');
select getDate();
select getUTCDate();

数学函数

-- 数学函数 
select pi();
select rand(100), rand(50), rand();
select round(rand(), 3), round(rand(100), 5);
select round(123.456, 2), round(254.124, -2);
select round(123.4567, 1, 2);

元数据

-- 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');

字符串函数

-- 字符串函数 
select ascii('a');
select ascii('A');
select char(97);
select char(65);
select nchar(65);
select nchar(45231);
select nchar(32993);
select unicode('A'), unicode('中');
select soundex('hello'), soundex('world'), soundex('word');
select patindex('%a', 'ta'), patindex('%ac%', 'jack'), patindex('dex%', 'dexjack');
select 'a' + space(2) + 'b', 'c' + space(5) + 'd';
select charIndex('o', 'hello world');
select charIndex('o', 'hello world', 6);
select quoteName('abc[]def'), quoteName('123]45');
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');
select difference('hello', 'world');
select difference('hello', 'llo');
select difference('hello', 'hel');
select difference('hello', 'hello');
select replace('abcedef', 'e', 'E');
select stuff('hello world', 3, 4, 'ABC');
select replicate('abc#', 3);
select subString('abc', 1, 1), subString('abc', 1, 2), subString('hello Wrold', 7, 5);
select len('abc');
select reverse('sqlServer'); 
select left('leftString', 4);
select left('leftString', 7);
select right('leftString', 6);
select right('leftString', 3);
select lower('aBc'), lower('ABC');
select upper('aBc'), upper('abc');
select ltrim(' abc'), ltrim('# abc#'), ltrim('  abc');
select rtrim(' abc    '), rtrim('# abc#   '), rtrim('abc');

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);

系统函数

-- 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 @@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;

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;

系统统计函数

-- 系统统计函数 
select @@CONNECTIONS;
select @@PACK_RECEIVED;
select @@CPU_BUSY;
select @@PACK_SENT;
select @@TIMETICKS;
select @@IDLE;
select @@TOTAL_ERRORS;
select @@IO_BUSY;
select @@TOTAL_READ;
select @@PACKET_ERRORS;
select @@TOTAL_WRITE;
select patIndex('%soft%', 'microsoft SqlServer');
select patIndex('soft%', 'software SqlServer');
select patIndex('%soft', 'SqlServer microsoft');
select patIndex('%so_gr%', 'Jsonisprogram');

自定义函数

-- 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);