PostgreSQL distinct 和 distinct on 区别
PostgreSQL About 1,179 words数据
city
空值的为null
z-blog=# select city, id, ip from ip_pool;
city | id | ip
--------+----+----------------
张家口 | 2 | 47.92.133.31
张家口 | 4 | 47.92.33.91
| 5 | 106.38.241.179
| 6 | 222.64.157.100
| 7 | 47.101.204.90
| 8 | 203.208.60.75
| 9 | 203.208.60.8
(7 行记录)
distinct
按city
,id
,ip
三个字段,组合唯一
z-blog=# select distinct city, id, ip from ip_pool;
city | id | ip
--------+----+----------------
张家口 | 2 | 47.92.133.31
张家口 | 4 | 47.92.33.91
| 5 | 106.38.241.179
| 6 | 222.64.157.100
| 7 | 47.101.204.90
| 8 | 203.208.60.75
| 9 | 203.208.60.8
(7 行记录)
distinct
可用all
代替。
z-blog=# select all city, id, ip from ip_pool;
city | id | ip
--------+----+----------------
张家口 | 2 | 47.92.133.31
张家口 | 4 | 47.92.33.91
| 5 | 106.38.241.179
| 6 | 222.64.157.100
| 7 | 47.101.204.90
| 8 | 203.208.60.75
| 9 | 203.208.60.8
(7 行记录)
distinct on
按city
为唯一
z-blog=# select distinct on(city) city, id, ip from ip_pool;
city | id | ip
--------+----+----------------
张家口 | 2 | 47.92.133.31
| 5 | 106.38.241.179
(2 行记录)
Views: 2,267 · Posted: 2021-01-05
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