Select the first row of a column in a group of rows within another column

问题

I have to display a list of the first row of a column within a group of rows within another column

Basic Query:

SELECT * FROM Table_Example cxp

My Table

    |plan   |code   |des   |month   |
----+-------+-------+------+--------+
    | 150B  | Alpha | etc.a| 1      |
----+-------+-------+------+--------+
    | 150B  | Beta  | etc.b| 2      |
----+-------+-------+------+--------+
    | 2600C | Alpha | etc.a| 6      |
----+-------+-------+------+--------+
    | 2600C | Alpha | etc.a| 7      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 3      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 7      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 9      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 2      |
----+-------+-------+------+--------+
    | 2600C | Gama  | etc.c| 4      |
----+-------+-------+------+--------+
    | 2600C | Gama  | etc.c| 12     |
----+-------+-------+------+--------+
    | 2600C | Delta | etc.d| 22     |
----+-------+-------+------+--------+
    | 42F   | Alpha | etc.a| 15     |

Expected Result

    |plan   |code   |des   |month   |
----+-------+-------+------+--------+
    | 2600C | Alpha | etc.a| 6      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 3      |
----+-------+-------+------+--------+
    | 2600C | Gama  | etc.g| 4      |
----+-------+-------+------+--------+
    | 2600C | Delta | etc.d| 22     |
----+-------+-------+------+--------+

Transcript Result: Having the variable '@plan', only show the rows that match that value (example: if '@plan' is 2600C) and within that group of rows, only show the first row of each different 'code' value

What i tried to do

SELECT * FROM Table_Example cxp WHERE plan = '2600C'

    |plan   |code   |des   |month   |
----+-------+-------+------+--------+
    | 2600C | Alpha | etc.a| 6      |
----+-------+-------+------+--------+
    | 2600C | Alpha | etc.a| 7      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 3      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 7      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 9      |
----+-------+-------+------+--------+
    | 2600C | Beta  | etc.b| 2      |
----+-------+-------+------+--------+
    | 2600C | Gama  | etc.c| 4      |
----+-------+-------+------+--------+
    | 2600C | Gama  | etc.c| 12     |
----+-------+-------+------+--------+
    | 2600C | Delta | etc.d| 22     |

But i can't get only the first row of each different 'code' I was thinking in a SubQuery but i tried a lot of them and i cant get the correct result or it returns only the 'code' column without the other columns like:

|code   |
+-------+
| Alpha |     
+-------+
| Beta  |       
+-------+
| Gama  |      
+-------+
| Delta |      
+-------+

回答1:

You can use row_number()

select * from
(
  SELECT *,row_number() over(partition by code order by month) as rnk
  FROM Table_Example cxp
  WHERE plan = '2600C'
)A where rnk=1

来源：https://stackoverflow.com/questions/64628483/select-the-first-row-of-a-column-in-a-group-of-rows-within-another-column

标签

sql

sql-server