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User-agent: mu4e 1.5.6; emacs 27.2
From: Roger Mason <rmason@mun.ca>
To: pgsql-novice <pgsql-novice@postgresql.org>
Subject: select from grouped data
Date: Wed, 25 Aug 2021 08:37:15 -0230
Message-ID: <y65sfyxdbq4.fsf@mun.ca>
MIME-Version: 1.0
Content-Type: text/plain
Archived-At: <https://www.postgresql.org/message-id/y65sfyxdbq4.fsf%40mun.ca>
Precedence: bulk

Hello,

I have written this function to process some multiline text data into a
table with both text & numeric columns:

CREATE OR REPLACE FUNCTION get_final_energy ()
  RETURNS TABLE (
    jid text,
    "timestamp" text,
    scf integer,
    energy double precision
  )
  AS $$
  WITH a AS (
    SELECT
      jid,
      regexp_split_to_table(totenergy_out, '\n') AS teo
    FROM
      results
),
b AS (
  SELECT
    results.jid,
    results. "timestamp",
    cast(
      CASE WHEN split_part(a.teo, ' ', 2) = '' THEN
        '0'
      ELSE
        split_part(a.teo, ' ', 2)
      END AS integer) AS scf,
    cast(
      CASE WHEN split_part(a.teo, ' ', 3) = '' THEN
        '0.0'
      ELSE
        split_part(a.teo, ' ', 3)
      END AS double precision) AS energy
  FROM
    results,
    a
  WHERE
    results.jid = a.jid
  GROUP BY
    results.jid,
    results. "timestamp",
    a.teo
  --HAVING
    -- scf = max(scf)
    ORDER BY
         timestamp ASC,
         scf DESC
)
SELECT
  *
FROM
  b;

$$
LANGUAGE sql;

The output looks like:

   jid     |    timestamp    | scf |     energy     
------------+-----------------+-----+----------------
 1250_1     | 20210805-114634 |  18 | -1316.43700819
 1250_1     | 20210805-114634 |  17 | -1316.43700825
 1250_1     | 20210805-114634 |  16 |  -1316.4370097
 1250_1     | 20210805-114634 |  15 | -1316.43700991
 1250_1     | 20210805-114634 |  14 | -1316.43699775
 1250_1     | 20210805-114634 |  13 | -1316.43699117
 1250_1     | 20210805-114634 |  12 | -1316.43750771
 1250_1     | 20210805-114634 |  11 | -1316.43805358
 1250_1     | 20210805-114634 |  10 | -1316.43857192
 1250_1     | 20210805-114634 |   9 | -1316.43070942
 1251_1     | 20210806-062539 |  18 | -1316.43700819
 1251_1     | 20210806-062539 |  17 | -1316.43700826
....

What I want is to get (for each group) the energy corresponding to the
maximum value of scf.

I appreciate any help,
Thanks,
Roger