MySQL

可能遇到的问题

[ERR] 2006 - MySQL server has gone away

问题描述

将MySQL8.0的脚本文件运行在MySQL5.7上，语句太长了：Your SQL statement was too large

解决方案

set global max_allowed_packet=1024*1024*160;

show global variables like 'max_allowed_packet'

参考链接

【1】https://blog.csdn.net/helloxiaozhe/article/details/78116871

 

三元运算符

语法：select *,if(expr1,expr2,expr3) from 表名

select QUARTER(time) AS quarter, b.category_id as categoryId, count(*) as count, if(b.category_id=0, sum(price_fixes), sum(price_install)) as sum from mt_contract a left join mt_fix_record b on a.mt_id=b.mt_id group by b.category_id, quarter