Question 267037 in Mysql Question posted in
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Mysql – Is it possible to combine these two SQL queries into one (WHERE, NULL, CASE)?

Is it possible to combine these two queries into one ?
Meaning: Take the first row if media_group is NULL,
otherwise take all rows with the same media_group

$get_first_record =  R::getRow( 'SELECT * FROM `prn` order by id asc  LIMIT 1');


if(isset($get_first_record['media_group'])){
    $get_media_records = R::getAll( 'SELECT * FROM `prn` WHERE media_group = '.$get_first_record['media_group']);
}

One SQL QUERY for simplify

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2

Answers


  1. 0

    We can consider using a union query along with a computed column. On MySQL:

    SELECT *
FROM
(
    (SELECT *, 1 AS src FROM prn ORDER BY id LIMIT 1)
    UNION ALL
    (SELECT *, 2 FROM prn WHERE media_group = ?)
) t
WHERE
    src = 1 AND media_group IS NULL
    OR
    src = 2;

    The logic here is to retain the single record from the first half of the union in case media_group be null (in which case the second half of the union would not return any records). Otherwise, keep only the second half of the union.

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  2. 0

    This is based on Tim’s answer but removing the need for the parameter:

    SELECT *
FROM
(
    (SELECT *, 1 AS src FROM prn ORDER BY id LIMIT 1)
    UNION ALL
    (
        SELECT *, 2
        FROM prn
        WHERE media_group IS NOT NULL
        AND media_group = (SELECT media_group FROM prn ORDER BY id LIMIT 1)
    )
) t
WHERE
    src = 1 AND media_group IS NULL
    OR
    src = 2;

    Here’s a db<>fiddle.

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