SQL--DISTINCT去重與GROUP BY的區別

1.查詢總的數據 1.1 SQL以下

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 查詢結果以下 2.GROUP BY的方式去重，條件是ORDER_ID 2.1SQL以下

#SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'
#GROUP BY的方式去重，條件是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 查詢結果以下 很明顯，invalid_flag=0的數據被去除掉了 3.DISTINCT方式去重 3.1 SQL以下

#SELECT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'
#GROUP BY的方式去重，條件是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 查詢結果以下

4.總結 方法2與方法3去重很明顯有區別 方法2採用的是單個條件ORDER_ID去重，而方法3採用的是ORDER_ID與INVAILD_FLAG 如下兩種方式去重結果同樣

#GROUP BY的方式去重，條件是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，條件是其後面全部的字段做爲一個總體再去重，而不是以靠近它的第一個字段做爲去重的條件
#SELECT DISTINCT tpc.ORDER_ID,tpc.INVAILD_FLAG FROM t_payment_code tpc WHERE tpc.ORDER_ID = '82487056720011566'