在 PostgreSQL 中，我如何 return 与值的最小值对应的整行？

Question

所以如果我有这样的table

id | value | detail
-------------------
12 | 20    | orange
12 | 30    | orange
13 | 16    | purple
14 | 50    | red
12 | 60    | blue

我怎样才能得到它return这个？

12 | 20 | orange
13 | 16 | purple
14 | 50 | red

如果我按 id 分组并详细说明 return 都是 12 | 20 |橙色和12 | 60 |蓝色

Answer 1

使用order by和limit:

select t.*
from table t
order by value
limit 1;

如果您在 value 上有一个索引，returns 所有匹配行的替代方法是：

select t.*
from table t
where value = (select min(value) from table t);

如果您只需要一行，则添加 limit。

Answer 2

这对于窗口聚合函数来说是一项简单的任务，ROW_NUMBER:

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

Answer 3

Postgres 有一个 DISTINCT ON 子句来解决这种情况。使用 DISTINCT ON (id)，查询将 return 仅为每个 id 值的第一条记录。您可以通过 ORDER BY 子句控制选择哪条记录。你的情况：

SELECT DISTINCT ON (id) *
FROM t
ORDER BY id, value

Answer 4

SQL Fiddle

PostgreSQL 9.3 架构设置:

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' );

查询 1:

不确定 Redshift 是否支持这种语法：

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 )

Results:

| id | value | detail |
|----|-------|--------|
| 12 |    20 | orange |
| 14 |    50 |    red |
| 13 |    16 | purple |

查询 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

Results:

| id | value | detail |
|----|-------|--------|
| 12 |    20 | orange |
| 13 |    16 | purple |
| 14 |    50 |    red |

在 PostgreSQL 中，我如何 return 与值的最小值对应的整行？

In PostgreSQL how can I return the entire row that corresponds with the min of a value?

sql

postgresql

min

amazon-redshift