#筛选每组比自己小的数量个数

select

t1.company,

t1.remark,

t1.score,

(select count(1) from sheet t2 where t1.remark=t2.remark and

t2.score

from sheet t1;

#分组统计比自身小的个数

select

a1.ipc,

a1.name,

a1.cishu,

(((select count(1) from a a2 where a1.ipc=a2.ipc and

a2.cishu

(select count(1) from a a2 where a1.ipc=a2.ipc and

a2.cishu=a1.cishu)/2)/(select count(cishu) from a a2 where

a1.ipc=a2.ipc)) count

from a a1;

#筛选前10条数据

select * from table_name limit 0,10

#从左边截取三个字符

create table bbb1

select inventor,ipc,jishu,left(ipc,3) as ipc1 from bbb

#合并同一字段的另一列数据，并存放在另一个表中

create table mygoods1

select cat_id,group_concat(distinct price separator ';') from

mygoods group by cat_id;

#去空格，替换

update bbb set ipc=replace(ipc,' ','')

#分组统计

create table `高校IPC大组统计`

select applicants,ipc_MainGroup,count(ipc_MainGroup) from

`统计结果2` group by applicants,ipc_MainGroup order by applicants

#删除score列字段为空的记录

delete from tb where `SCORE` is NULL

#删除score为90的记录

delete from tb where `SCORE` = 90

#方法一、去重 对name和type相同的数值去重，并筛选出id最小的一列

select id,name,type from sheet1

where id in(select min(id) from sheet1 group by name);

#创建一个临时表进行判断

create table sheet3

select *,case type when '大型企业' then '4' when '中型企业' then

'3'

when '中小型企业' then '2' when '小微型企业' then '1' else '0' end as

type1 from sheet1;

#新建一个表，存放结果

create table sheet6

select name,type,source,max(type1) from sheet3 group by

name;

#用max选择最大的，建一个虚拟表sheet4，然后再left outer

join关联其他字段，并将查询的结果存放到sheet5中

create table sheet5

select sheet4.*,sheet3.type from

(select name,max(type1) as type2 from sheet3 group by name) as

sheet4 left outer join

sheet3 on sheet4.name=sheet3.name and

sheet4.type2=sheet3.type1;

#查询每组的前n条记录，此处为前三条记录，修改数字3即可筛选另外前N条记录

#查询每个分类中价格最高的两个商品

SELECT mygoods1.* FROM mygoods mygoods1

WHERE

(SELECT count(*) FROM mygoods WHERE cat_id=mygoods1.cat_id AND

price> mygoods1.price)< 3

ORDER BY mygoods1.cat_id,mygoods1.price DESC;

#合并时去重，并用分号隔开(默认隔开符号为逗号)

select cat_id,group_concat(distinct price separator ';') from

mygoods group by cat_id;

#以cat_id分组，把price字段的值打印在一行，逗号分隔，按照price倒序排列

select cat_id,group_concat(price order by price desc) from

mygoods group by cat_id;

#批量加数字,2列合并成一列

update id17 set inventor = concat(id,inventor)

#批量逗号转化为id+逗号

update id17 set inventor =

replace(inventor,',',CONCAT(',',id))

查找出表mygoods的goods_id不在mygoods2中的记录

select * from mygoods where goods_id not in (select goods_id

from mygoods2);

#查询usedname这一列不为空的记录

#方法一

select * from companyname where usedname is not null;

#方法二

select * from table where usedname <> "";

select * from table where usedname != "";

#查询为空的记录

select * from table where id ="";

select * from table where isNull(id);

#具体情况具体分析，如果字段是char或者varchar类型的，使用id=""可以的；

#如果字段是int类型的，使用isNull会好些。

#查询表

SELECT * FROM `企业指标_标准化名称_20190703` WHERE tech_name is not

null limit 10

#去除空格

update 表 set 列名 =replace(列名,' ','')

#去除name字段末尾的逗号

update 表名 set name=left(name,char_length(name)-1) where

right(name,1)=','

#null值替换为0

select IFNULL(列名,0) from 表名

#空字符串替换为0

select IF(数据2,数据2,0) from test

#MySQL随机取一条记录(并列随机取1个)

select a.* from 表名 a where code = (select code from 表名 where

count = a.count limit 1) order by a.count

#按name分组取val最大的值所在行的数据

select a.* from tb a where val = (select max(val) from tb

where name = a.name) order by a.name

#按name分组取val最大的值所在行的数据

select a.* from tb a where val = (select min(val) from tb

where name = a.name) order by a.name

#按name分组取第一次出现的行所在的数据

select a.* from tb a where val = (select val from tb where

name = a.name limit 1) order by a.name