qq_41889508的博客

MySql5.7及以上 GROUP BY 报错问题，因为SELECT 查询中的非聚合列没有明确地出现在 GROUP BY 子句中，执行sql报错如下：which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

dbeaver导入导出数据库（sql文件形式）

select from where left join/right join/inner join/full join/cross join on where group by having order by limit 以及union/union all关键词，执行顺序和原理，聚合函数，例如max(),最小值min(),平均值avg()计数count()求和sum()，子查询分为相关子查询和非相关子查询，in，exists，not in，not exists 分组后每组显示前几条数据，模拟窗口函数进行优化