Find the first key by date field using sql and output also have other fields

问题

I want to query the first occurrence of every name according to the earliest date. The output should have the complete row. Please help me to write the query in sql.

Input:

  Name |    ID |    payment_date |  Pack
 ------+-------+-----------------+-------
    A  |    11 |    31-Jan       |  P
    C  |    13 |    31-Jan       |  Q
    B  |    2  |    31-Jan       |  R
    C  |    3  |    28-Jan       |  P
    D  |    23 |    29-Jan       |  Q
    B  |    11 |    30-Jan       |  R
    A  |    17 |    25-Jan       |  P
    C  |    13 |    26-Jan       |  Q
    D  |    17 |    2-Feb        |  R
    B  |    23 |    3-Feb        |  P
    A  |    45 |    4-Feb        |  Q
    B  |    3  |    5-Feb        |  R

Output:

  Name |    ID | payment_date | Pack
  -----+-------+--------------+-----
    A  |    17 | 25-Jan       | P
    B  |    11 | 30-Jan       | R
    C  |    13 | 26-Jan       | Q
    D  |    23 | 29-Jan       | Q

回答1:

You can use the min function, also assuming payment_date is a date type:

select Name, ID, min(payment_date), Pack from mytable
group by payment_date,Name, ID, Pack
order by Name

The downfall about this method is putting all of the fields in the group by.

回答2:

If your payment_date is a date data type, you can use not exists() like so:

select *
from t
where not exists (
  select 1
  from t i
  where i.Name = t.Name
    and i.payment_date < t.payment_date
    )

rextester demo (sql server): http://rextester.com/OKB46268

returns

+------+----+-------------+------+
| Name | Id | PaymentDate | Pack |
+------+----+-------------+------+
| A    | 17 | 2017-01-25  | P    |
| B    | 11 | 2017-01-30  | R    |
| C    | 13 | 2017-01-26  | Q    |
| D    | 23 | 2017-01-29  | Q    |
+------+----+-------------+------+

回答3:

You can also use Vertica's enhanced LIMIT clause:

WITH
-- input, don't use in real query
input(Name,ID,payment_date,Pack) AS (
          SELECT 'A',11,DATE '31-Jan-2017','P'
UNION ALL SELECT 'C',13,DATE '31-Jan-2017','Q'
UNION ALL SELECT 'B',2, DATE '31-Jan-2017','R'
UNION ALL SELECT 'C',3, DATE '28-Jan-2017','P'
UNION ALL SELECT 'D',23,DATE '29-Jan-2017','Q'
UNION ALL SELECT 'B',11,DATE '30-Jan-2017','R'
UNION ALL SELECT 'A',17,DATE '25-Jan-2017','P'
UNION ALL SELECT 'C',13,DATE '26-Jan-2017','Q'
UNION ALL SELECT 'D',17,DATE  '2-Feb-2017','R'
UNION ALL SELECT 'B',23,DATE  '3-Feb-2017','P'
UNION ALL SELECT 'A',45,DATE  '4-Feb-2017','Q'
UNION ALL SELECT 'B',3, DATE  '5-Feb-2017','R'
)
-- end of input , start real query here:
SELECT * FROM input
LIMIT 1 OVER(PARTITION BY Name ORDER BY payment_date)
;

Happy playing ... Marco the Sane

来源：https://stackoverflow.com/questions/44167796/find-the-first-key-by-date-field-using-sql-and-output-also-have-other-fields

标签

sql

greatest-n-per-group

vertica