案例:在查询每个事项id的同时,对事项所属company下的所有事项进行统计
一、group by
说明:group by company:对company进行分组,需要注意的是group by后面必须要带着除聚合函数外所有要查询的列
SELECT id,company,count(company) from ITEM_MAIN_LIST group by company,id
效果图
总结:由查询结果可知,在查出每个事项id的同时,无法做到对相同company的统计
二、COUNT (*) OVER (PARTITION BY)
说明:COUNT (id) OVER (PARTITION BY company) :根据company对id进行计数/统计
SELECT id,company,COUNT (ID) OVER (PARTITION BY company) AS num FROM ITEM_MAIN_LIST