MySQL中数据查询语句整理大全(mysql中数据查询语句整理大全是什么)满满干货

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目录一、基本概念(查询语句)①基本语句②条件查询二、总结1、普通查询2、去重查询(distinct)3、排序查询(order by)4、分组查询(group by)5.等值查询6.外连接查询7.内连接查询8.合并查询总结

1、“select * from 表名;”,—可查询表中全部数据;

2、“select 字段名 from 表名;”,—可查询表中指定字段的数据;

3、“select distinct 字段名 from 表名;”,—可对表中数据进行去重查询。

4、“select 字段名 from 表名 where 查询条件;”,—可根据条件查询表中指定字段的数据;

1)比较运算符:>, <, >=, <=,=, !=, <>

查询大于18岁的信息

select * from students where age>18;
select id, name,gender from students where age>18;

查询小于18岁的信息

select * from students where age<18;

查询年龄为18岁的所有学生的名字

select * from students where age=18;

2)逻辑运算符:and, or, not

–18到28之间的学生信息

select * from students where age>18_and age<28:

–18岁以上的女性

select * from students where age>18 and gender=”女”;
select * from students where age>18 and gender=2;

–18以上或者身高查过180(包含)以上

select * from students where age>18 or height>=180;

不在18岁以上的女性这个范围内的信息

select * from students where not (age>18 and gender=2);

年龄不是小于或者等于18并且是女性

select * from students where (not age<=18) and gender=2;

3)模糊查询:like, rlike

% 替换1个或者多个

_ 替换1个

查询姓名中 以“小”开始的名字

select name from students where name=”小”;
select name from students where name like”小%”;

查询姓名中有“小”所有的名字

select name from students whece name like “%小%”;

查询有2个字的名字

select name from students where name like “__”;

查询有3个字的名字

select name from students where name like “__”;

查询至少有2个字的名字 select name from

students where name like “__%”;

rlike正则

查询以周开始的姓名

select name from students where name rlike “^周.*”;

查询以周开始、伦结尾的姓名

select name from students where name rlike “^周.*伦$”;

4)范围查询:in,not in,between…and,not between…and

查询年龄为18、34的姓名

select name, age from students where age=18 or age=34;
select name,age from students where age in (18,34);

not in不非连续的范围之内

年龄不是 18、34岁之间的信息

select name,age from students where age not in (18,34);

between … and …表示在一个连续的范围内

查询年龄在18到34之间的的信息

select name,age from students where age between 18 and 34;

not between … and …表示不在一个连续的范围内

查询年龄不在在18到34之间的的信息

select * from students where age not between 18 and 34;

空判断

判空 is null

查询身高为空的信息

select *from students where height is null/NULL/Null;

判非空is not null

select * from students where height is not null;

排序:order_by

–查询年龄在18到34岁之间的男性,按照年龄从小到大排序

select * from students where (age between 18 and 34) and gender=1;
select * from students where (age between 18 and 34) and gender=1 order by age;
select * from students where (age between 18 and 34) and gender=1 order by age asc;

查询年龄在18到34岁之间的女性,身高从高到矮排序

select * from students where (age between18 and 34) and gender=2 order by height desc;

order by多个字段

查询年龄在18到34岁之间的女性,身高从高到矮排序,如果身高相同的情况下按照年龄从小到大排序

select * from students where (age between 18 and 34) and gender=2 order by height desc,age asc;

查询年龄在18到34岁之间的女性,身高从高到矮排序,如果身高相同的情况下按照年龄从小到大排序,如果年龄也相同那么按照id从大到小排序

select * from students where (age between 18 and 34) and gender=2 order by height desc,age asc, id desc;

按照年龄从小到大、身高从高到矮的排序

select * from students order by age asc,height desc;

分组:group_by, group_concat():查询内容, having

where :是对整个数据表信息的判断;

having:是对于分组后的数据进行判断

–group by

按照性别分组,查询所有的性别

select gender from students group by gender;

–计算每种性别中的人数

select gender, count(*) from students group by gender;

where是在group by 前面

–计算男性的人数

select count(*) from students where gender=’男’;

–group_concat(…)

查询同种性别中的姓名

select gender,group_concat(name) from students group by gender;

having :having是在group by后面

查询平均年龄超过30岁的性别,以及姓名

select gender ,avg(age) from students group by gender having avg(age) > 30;

查询每种性别中的人数多于2个的信息

select gender,count(*) from students group by gender having count(*) > 2;

– 查询每组性别的平均年龄

select gender,avg(age) from students group by gender;

分页: limit

limit start,count (start:表示从哪─个开始;count:表示数量)
即limit(第N页-1)*每个的个数,每页的个数;
limit在使用的时候,要放在最后面.

限制查询出来的数据个数

select *from students where gender=1 limit 2;

查询前5个数据

select* from students limit 0,5;

查询id6-10(包含)的书序

select * from students limit 5,5;

每页显示2个,第1个页面

select * from students limit 0,2;

每页显示2个,第2个页面

select * from students limit 2,2;

每页显示2个,第3个页面

select * from students limit 4,2;

每页显示2个,第4个页面

select * from students limit 6,2;

每页显示2个,显示第6页的信息,按照年龄从小到大排序

select * from students order by age asc limit 10,2;

– 如果重新排序了,那么会显示第一页

select * from students where gender=2 order by height des limit 0,2;

5)聚合函数:count(), max(), min(), sum(), avg(), round()

聚合函数

-总数– count

-查询男性有多少人,女性有多少人

select count(*) from students where gender=1;
select count(*) as 男性人数 from students where gender=1;
select count(*) as 女性人数 from students where gender=2;

-最大值-最小值

– max –min

一查询最大的年龄

select max (age) from students;

–查询女性的最高身高

select max (height) from students where gender=2;

-求和

–sum

-计算所有人的年龄总和

select sum ( age) from students;

–平均值

– avg

–计算平均年龄

select avg(age) from students;

–计算平均年龄

select sum ( age) / count(* ) from students;

–四舍五入round ( 123.23 ,_1)保留1位小数

–计算所有人的平均年龄,保留2位小数

select round (sum(age)/count(*),2) from students; select round ( sum(age)/count(*),3) from students ;

–计算男性的平均身高保留2位小数

select round(avg (height),2) from students where gender=1; select name,round(avg(height),2) from students where gender=1;

6)连接查询 :inner join, left join, right join

inner join

select … from 表 A inner join表B;

select * from students inner join classes;

查询有能够对应班级的学生以及班级信息

select * from students inner join classes on students.cls_id=classes.id;

按照要求显示姓名、班级

select students.*, classes.name from students inner join classes on students.cls_id=classes.id;
select students.name,classes.name from students inner join classes on students.cls_id=classes.id;

给数据表起名字

select s.name,c.name from students as s inner join classes as c on s.cls_id=c.id;

查询有能够对应班级的学生以及班级信息,显示学生的所有信息,只显示班级名称

select s.*,c.name from students as s inner join classes as c on s.cls_id=c.id;

在以上的查询中,将班级姓名显示在第1列

select c.name,s.* from students as s inner join classes as c on s.cls_id=c.id;

查询有能够对应班级的学生以及班级信息,按照班级进行排序

select c.xxx s.xxx from student as s inner join clssses as c on … order by …;

select c.name,s.* from students as s inner join classes as c on s.cls_id=c.id order by c.name;

当时同一个班级的时候,按照学生的id进行从小到大排序

select c.name,s.* from students as s inner join classes as c on s.cls_id=c.id order by c.name,s.id;

left join

查询每位学生对应的班级信息

select * from students as s left join classes as c on s.cls_id=c.id;

查询没有对应班级信息的学生

– select … from xxx as s left join xxx as c on… where …

– select … from xxx as s left join xxx as c on… . … having …

select * from students as s left join classes as c on s.cls_id=c.id having c.id is null;
select * from students as s left join classes as c on s.cls_id=c.id where c.id is null;

left join是按照左边的表为基准和右边的表进行查询,查到就显示,查不到就显示为null

补充

查询所有字段:select * from 表名; 

查询指定字段:select 列1,列2,… from 表名; 

使用 as 给字段起别名: select 字段 as 名字…. from 表名; 

查询某个表的某个字段:select 表名.字段 …. from表名; 

可以通过 as 给表起别名: select 别名.字段 …. from 表名 as 别名; 

消除重复行: distinct 字段

注意:WHERE子句中是不能用聚集函数作为条件表达式的!

(1)命令:select * from <表名>;

(2)命令:select <要查询的字段> from <表名>;

命令:select distinct <要查询的字段> from <表名>

升序:asc

降序:desc

降序排列命令:select <要查询的字段名> from <表名> order by <要查询的字段名> desc

不加desc一般默认为升序排列

命令:select <按什么分的组>, Sum(score) from <表名> group by <按什么分的组>

假设现在又有一个学生成绩表(result)。要求查询一个学生的总成绩。我们根据学号将他们分为了不同的组。

命令:

select id, Sum(score)
from result
group by id;

现在有两个表学生表(stu)和成绩表(result)。

当连接运算符为“=”时,为等值连接查询。

现在要查询年龄小于20岁学生的不及格成绩。

select stu.id,score
from stu,result
where stu.id=result.id and age < 20 and score < 60;

等值查询效率太低

①语法

select f1,f2,f3,….
from table1 left/right outer join table2
on 条件;

②左外连接查询,例如

select a.id,score
from
(select id,age from stu where age < 20) a (过滤左表信息)
left join
(select id, score from result where score < 60) b (过滤右表信息)
on a.id=b.id;

左外连接就是左表过滤的结果必须全部存在。如果存在左表中过滤出来的数据,右表没有匹配上,这样的话右表就会出现NULL;

③右外连接查询,例如

select a.id,score
from
(select id,age from stu where age < 20) a (过滤左表信息)
right join
(select id, score from result where score < 60) b (过滤右表信息)
on a.id=b.id;

右外连接就是左表过滤的结果必须全部存在

①语法

select f1,f2,f3,….
from table1 inter join table2
on 条件;

②例如

select a.id,score
from
(select id,age from stu where age < 20) a (过滤左表信息)
inner join
(select id, score from result where score < 60) b (过滤右表信息)
on a.id=b.id;

在图书表(t_book)和图书类别表(t_bookType)中

①.union

使用union关键字是,数据库系统会将所有的查询结果合并到一起,然后去掉相同的记录;

select id
from t_book
union
select id
from t_bookType;

②.union all

使用union all,不会去除掉重复的记录;

select id
from t_book
union all
select id
from t_bookType;

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