sql中的字符串匹配、函数⼤全1.语法基础选调生考试时间2021
2.⾼级语法编程
3.⾼级查询
⾼级查询在数据库中⽤得是最频繁的，也是应⽤最⼴泛的。
Ø 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 top3*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 >2and sex =1;
--or 或者
select*from student where id =2or sex =1;
--between ... and ... 相当于并且
select*from student where id between2and5;
select*from student where id not between2and5;
--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 >2group 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 >2group 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 >1and 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。
# 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 >2and 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 (
2015国考申论副省级答案解析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
);新疆招生考试信息网
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 =5and age >all (
select age from student where cid =3
);
select*from student where cid =5and age >any (
select age from student where cid =3
);
select*from student where cid =5and 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
广东公务员成绩对年龄⼤于的进⾏汇总
select age from student
where age >20order 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 >20order by sex, age compute sum(age) by sex;
按照年龄分组汇总
select age from student
where age >20order by age, id compute sum(age);
按照年龄分组，年龄汇总，id最⼤值
select id, age from student
where age >20order 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;
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 ntile2021年广东公务员考试职位表
from student s, classes c where cid = c.id;
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%';
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。
--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;
Ø 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;
Ø 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
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
邓州招聘网最新招聘信息网--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');--查索引
select charIndex('o', 'hello world', 6);--查索引
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');
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