mysql 常见使用场景

场景1：表中多条相同账户数据，根据创建日期排序取第一条。

select * from cms_client_rpq rpq
	where id = (
	select  id from cms_client_rpq 
	   where cif_no = rpq.cif_no 
		 order by create_time desc 
		 limit 1 
	)

场景2.primary key 不区分大小写

ALTER TABLE `cms_rpq_risk_report` 
CHANGE COLUMN `accountid` `accountid` VARCHAR(50) binary primary key ;//设置为binary 

场景3.将表A 中的字段col_a，更新到表B 的字段col_b,用表A的id，关联表B 的p_id

update A a,B b set b.col_b=a.col_a
where b.p_id=a.id

场景4.查找某个字符串中，某个字段出现的次数

length(accountids)-length(replace(accountids,'#','')) length

场景5.动态行转列

原表数据样式:

将不同时间段受教育时间转成列:

select 
educate.user_id,
educate.user_name,
college.start_time college_start_time,
college.end_time college_end_time,
senior.start_time senior_start_time,
senior.end_time senior_end_time
from 
(select distinct user_id,user_name from user_educate_base_info) educate
left join user_educate_base_info college on college.user_id=educate.user_id and college.education='college'
left join user_educate_base_info senior on senior.user_id=educate.user_id and senior.education='senior'