[英]In PostgreSQL how can I return the entire row that corresponds with the min of a value?
所以如果我有這樣的桌子
id | value | detail
-------------------
12 | 20 | orange
12 | 30 | orange
13 | 16 | purple
14 | 50 | red
12 | 60 | blue
我如何獲得退貨?
12 | 20 | orange
13 | 16 | purple
14 | 50 | red
如果按ID和明細分組,則返回12 | 20 | 橙色和12 | 60 | 藍色
PostgreSQL 9.3模式設置 :
CREATE TABLE TEST( id INT, value INT, detail VARCHAR );
INSERT INTO TEST VALUES ( 12, 20, 'orange' );
INSERT INTO TEST VALUES ( 12, 30, 'orange' );
INSERT INTO TEST VALUES ( 13, 16, 'purple' );
INSERT INTO TEST VALUES ( 14, 50, 'red' );
INSERT INTO TEST VALUES ( 12, 60, 'blue' );
查詢1 :
不確定Redshift是否支持以下語法:
SELECT DISTINCT
FIRST_VALUE( id ) OVER wnd AS id,
FIRST_VALUE( value ) OVER wnd AS value,
FIRST_VALUE( detail ) OVER wnd AS detail
FROM TEST
WINDOW wnd AS ( PARTITION BY id ORDER BY value )
結果 :
| id | value | detail |
|----|-------|--------|
| 12 | 20 | orange |
| 14 | 50 | red |
| 13 | 16 | purple |
查詢2 :
SELECT t.ID,
t.VALUE,
t.DETAIL
FROM (
SELECT *,
ROW_NUMBER() OVER ( PARTITION BY ID ORDER BY VALUE ) AS RN
FROM TEST
) t
WHERE t.RN = 1
結果 :
| id | value | detail |
|----|-------|--------|
| 12 | 20 | orange |
| 13 | 16 | purple |
| 14 | 50 | red |
對於窗口匯總函數ROW_NUMBER,這是一項簡單的任務:
select *
from
(
select t.*,
row_number()
over (partition by id -- for each id
order by value) as rn -- row with the minimum value
from t
) as dt
where rn = 1
Postgres有一個DISTINCT ON
子句來解決這種情況。 使用DISTINCT ON (id)
,查詢將僅返回每個id
值的第一條記錄。 您可以控制通過ORDER BY
子句選擇的記錄。 在您的情況下:
SELECT DISTINCT ON (id) *
FROM t
ORDER BY id, value
使用order by
limit
:
select t.*
from table t
order by value
limit 1;
如果您在value
上有一個索引,則返回所有匹配行的替代方法是:
select t.*
from table t
where value = (select min(value) from table t);
如果只需要一行,則添加一個limit
。
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