SQL--DISTINCT去重与GROUP BY的区别

时间 2019-11-05

标签 sql distinct group 区别栏目 SQL 繁體版

原文原文链接

1.查询总的数据 1.1 SQL以下code

SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'
#SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566' GROUP BY tpc.ORDER_ID
#SELECT DISTINCT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'

1.2 查询结果以下 2.GROUP BY的方式去重，条件是ORDER_ID 2.1SQL以下图片

#SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'
#GROUP BY的方式去重，条件是ORDER_ID
SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566' GROUP BY tpc.ORDER_ID
#SELECT DISTINCT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'

2.2 查询结果以下很明显，invalid_flag=0的数据被去除掉了 3.DISTINCT方式去重 3.1 SQL以下it

#SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'
#GROUP BY的方式去重，条件是ORDER_ID
#SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566' GROUP BY tpc.ORDER_ID
#DISTINCT方式去重
SELECT DISTINCT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'

3.2 查询结果以下方法

4.总结方法2与方法3去重很明显有区别方法2采用的是单个条件ORDER_ID去重，而方法3采用的是ORDER_ID与INVAILD_FLAG 如下两种方式去重结果同样im

#GROUP BY的方式去重，条件是ORDER_ID、INVAILD_FLAG
SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566' GROUP BY tpc.ORDER_ID,tpc.INVAILD_FLAG
#DISTINCT方式去重，条件是其后面全部的字段做为一个总体再去重，而不是以靠近它的第一个字段做为去重的条件
#SELECT DISTINCT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'