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 (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;

-- 日期时间函数 

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 

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 

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 

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

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;

select @@version; // 当前数据库版本信息

-- 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');

-- 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);