postgresql rank() over, dense_rank(), row_number()用法區別
阿新 • • 發佈：2020-12-29
如下學生表student，學生表中有姓名、分數、課程編號，需要按照課程對學生的成績進行排序
select * from jinbo.student; id | name | score | course ----+-------+-------+-------- 5 | elic | 70 | 1 4 | dock | 100 | 1 3 | cark | 80 | 1 2 | bob | 90 | 1 1 | alice | 60 | 1 10 | jacky | 80 | 2 9 | iris | 80 | 2 8 | hill | 60 | 1 7 | grace | 50 | 2 6 | frank | 70 | 2 6 | test | | 2 (11 rows)
1、rank over () 可以把成績相同的兩名是並列，如下course = 2 的結果rank值為：1 2 2 4 5
select name,score,course,rank() over(partition by course order by score desc) as rank from jinbo.student; name | score | course | rank -------+-------+--------+------ dock | 100 | 1 | 1 bob | 90 | 1 | 2 cark | 80 | 1 | 3 elic | 70 | 1 | 4 hill | 60 | 1 | 5 alice | 60 | 1 | 5 test | | 2 | 1 iris | 80 | 2 | 2 jacky | 80 | 2 | 2 frank | 70 | 2 | 4 grace | 50 | 2 | 5 (11 rows)
2、dense_rank()和rank over()很相似，可以把學生成績並列不間斷順序排名，如下course = 2 的結果rank值為：1 2 2 3 4
select name,dense_rank() over(partition by course order by score desc) as rank from jinbo.student; name | score | course | rank -------+-------+--------+------ dock | 100 | 1 | 1 bob | 90 | 1 | 2 cark | 80 | 1 | 3 elic | 70 | 1 | 4 hill | 60 | 1 | 5 alice | 60 | 1 | 5 test | | 2 | 1 iris | 80 | 2 | 2 jacky | 80 | 2 | 2 frank | 70 | 2 | 3 grace | 50 | 2 | 4 (11 rows)
3、row_number 可以把相同成績的連續排名，如下 course = 2 的結果rank值為：1 2 3 4 5
select name,row_number() over(partition by course order by score desc) as rank from jinbo.student; name | score | course | rank -------+-------+--------+------ dock | 100 | 1 | 1 bob | 90 | 1 | 2 cark | 80 | 1 | 3 elic | 70 | 1 | 4 hill | 60 | 1 | 5 alice | 60 | 1 | 6 test | | 2 | 1 iris | 80 | 2 | 2 jacky | 80 | 2 | 3 frank | 70 | 2 | 4 grace | 50 | 2 | 5 (11 rows)
使用rank over()的時候，空值是最大的，如果排序欄位為null,可能造成null欄位排在最前面，影響排序結果，可以如下：
rank over(partition by course order by score desc nulls last)
4、總結
partition by 用於結果集分組，如果沒有指定，會把整個結果集作為一個分組
rank 、dense_rank 、row_numer 都是不同方式的結果集組內排序，一般都結合over 字句出現，over 字句裡 會有 partition by、order by、last、first 的任意組合，如下：
rank() over(partition by a,b order by a,order by b desc); rank() over(partition by a order by b nulls first) rank() over(partition by a order by b nulls last)
補充：Oracle或者PostgreSQL的row_number over 排名語法
PostgreSQL 和Oracle 都提供了 row_number() over() 這樣的語句來進行對應的欄位排名，很是方便。MySQL卻沒有提供這樣的語法。
這次我提供的表結構如下，
Table "ytt.t1"
Column | Type | Modifiers
--------+-----------------------+-----------
i_name | character varying(10) | not null
rank | integer | not null
我模擬了20條資料來做演示。
t_girl=# select * from t1 order by i_name; i_name | rank ---------+------ Charlie | 12 Charlie | 12 Charlie | 13 Charlie | 10 Charlie | 11 Lily | 6 Lily | 7 Lily | 7 Lily | 6 Lily | 5 Lily | 7 Lily | 4 Lucy | 1 Lucy | 2 Lucy | 2 Ytt | 14 Ytt | 15 Ytt | 14 Ytt | 14 Ytt | 15 (20 rows)
在PostgreSQL下，我們來對這樣的排名函式進行三種不同的執行方式1：
第一種：
完整的帶有排名欄位以及排序。
t_girl=# select i_name,rank,row_number() over(partition by i_name order by rank desc) as rank_number from t1; i_name | rank | rank_number ---------+------+------------- Charlie | 13 | 1 Charlie | 12 | 2 Charlie | 12 | 3 Charlie | 11 | 4 Charlie | 10 | 5 Lily | 7 | 1 Lily | 7 | 2 Lily | 7 | 3 Lily | 6 | 4 Lily | 6 | 5 Lily | 5 | 6 Lily | 4 | 7 Lucy | 2 | 1 Lucy | 2 | 2 Lucy | 1 | 3 Ytt | 15 | 1 Ytt | 15 | 2 Ytt | 14 | 3 Ytt | 14 | 4 Ytt | 14 | 5 (20 rows)
第二種：
帶有完整的排名欄位但是沒有排序。
t_girl=# select i_name,row_number() over(partition by i_name ) as rank_number from t1; i_name | rank | rank_number ---------+------+------------- Charlie | 12 | 1 Charlie | 12 | 2 Charlie | 13 | 3 Charlie | 10 | 4 Charlie | 11 | 5 Lily | 6 | 1 Lily | 7 | 2 Lily | 7 | 3 Lily | 6 | 4 Lily | 5 | 5 Lily | 7 | 6 Lily | 4 | 7 Lucy | 1 | 1 Lucy | 2 | 2 Lucy | 2 | 3 Ytt | 14 | 1 Ytt | 15 | 2 Ytt | 14 | 3 Ytt | 14 | 4 Ytt | 15 | 5 (20 rows)
第三種：
沒有任何排名欄位，也沒有任何排序欄位。
t_girl=# select i_name,row_number() over() as rank_number from t1; i_name | rank | rank_number ---------+------+------------- Lily | 7 | 1 Lucy | 2 | 2 Ytt | 14 | 3 Ytt | 14 | 4 Charlie | 12 | 5 Charlie | 13 | 6 Lily | 7 | 7 Lily | 4 | 8 Ytt | 14 | 9 Lily | 6 | 10 Lucy | 1 | 11 Lily | 7 | 12 Ytt | 15 | 13 Lily | 6 | 14 Charlie | 11 | 15 Charlie | 12 | 16 Lucy | 2 | 17 Charlie | 10 | 18 Lily | 5 | 19 Ytt | 15 | 20 (20 rows)
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