Re: A complex SQL query - Mailing list pgsql-sql

From Jānis Pūris
Subject Re: A complex SQL query
Date
Msg-id d1ed2c23-e5ea-4eab-adc9-75ec12ec7038@Spark
Whole thread Raw
In response to A complex SQL query  ("jj08" <jj08@drivehq.com>)
List pgsql-sql
Would something like this work for you ? http://www.sqlfiddle.com/#!17/2e45eb/9

select
    user_id,
    max(start_date) as start_date,
    case when max(end_date) < max(start_date) then null else max(end_date) end as end_date
from
    employment
where
    employer = 'Micro'
group by
    user_id
;
On 6 Sep 2019, 14:31 +0200, jj08 <jj08@drivehq.com>, wrote:

 I hope someone can give me some pointers.

Here is my table.

+--------+----------+------------+-----------+

| usr_id | employer | start_date | end_date  |

+--------+----------+------------+-----------+

| A      | Goo      | 201904     | -         |

| A      | Micro    | 201704     | 201903    |

 

| B      | Micro    | 201706     | -         |

| B      | Goo      | 201012     | 201705    |

| B      | Micro    | 201001     | 201011    |

+--------+----------+------------+-----------+

 

I am trying to list up people working for a company called "Micro".

Some people work for a company multiple times, like user B.

I only need one line per user, displaying only the latest affiliation date.

 

For user_id "B", I could do Select user_id, MAX(start_date), end_date where employer = 'Micro',

but that would fail to get record for user_id "A".

 

If multiple records exist, I want to do MAX, but if only a single record exists, I don't need MAX.

How do I do that? 

From the above data, I would like to see only two lines:

| A      | Micro    | 201704     | 201903    |

| B      | Micro    | 201706     | -         |

Thank you.


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