Как да подредите и групирате MySQL резултати

Ето валиден резултат за по-прост проблем.

• 1 сутрин, 1 следобед, 1 вечер и 1 нощна „смяна“
• сума от 'ставката' <50
• AA и BB (единствените възможни стойности) трябва да се появят по два пъти

      
    DROP TABLE IF EXISTS my_table;
    
    CREATE TABLE my_table
    (id SERIAL PRIMARY KEY
    ,code CHAR(2) NOT NULL
    ,shift VARCHAR(12) NOT NULL
    ,rate INT NOT NULL
    );
    
    INSERT INTO my_table VALUES
    ( 1 , 'AA' , 'Morning'   , 10),
    ( 2 , 'BB' , 'Afternoon' , 20),
    ( 3 , 'AA' , 'Evening'   , 13),
    ( 4 , 'BB' , 'Night'     , 18),
    ( 5 , 'BB' , 'Morning'   , 15),
    ( 6 , 'AA' , 'Afternoon' , 25),
    ( 7 , 'BB' , 'Evening'   , 15),
    ( 8 , 'AA' , 'Night'     , 22),
    ( 9 , 'AA' , 'Morning'   , 10),
    (10 , 'BB' , 'Afternoon' , 20),
    (11 , 'AA' , 'Evening'   , 13),
    (12 , 'AA' , 'Night'     , 18),
    (13 , 'BB' , 'Morning'   , 15),
    (14 , 'BB' , 'Afternoon' , 25),
    (15 , 'AA' , 'Evening'   , 15),
    (16 , 'BB' , 'Night'     , 22),
    (17 , 'AA' , 'Morning'   , 10),
    (18 , 'BB' , 'Afternoon' , 20),
    (19 , 'BB' , 'Evening'   , 13),
    (20 , 'AA' , 'Night'     , 18),
    (21 , 'AA' , 'Morning'   , 15),
    (22 , 'BB' , 'Afternoon' , 25),
    (23 , 'AA' , 'Evening'   , 15),
    (24 , 'BB' , 'Morning'   , 10),
    (25 , 'BB' , 'Afternoon' ,  2),
    (26 , 'AA' , 'Evening'   ,  8),
    (27 , 'BB' , 'Night'     ,  3),
    (28 , 'AA' , 'Morning'   ,  5),
    (29 , 'BB' , 'Afternoon' ,  2),
    (30 , 'AA' , 'Evening'   ,  1),
    (31 , 'BB' , 'Night'     ,  2),
    (32 , 'AA' , 'Night'     ,  2);
    
        SELECT * -- for simplicity. In reality, we would need to name and alias all columns for this result to be usable
          FROM my_table morning1
          JOIN my_table afternoon1
            ON afternoon1.id <> morning1.id 
          JOIN my_table evening1 
            ON evening1.id NOT IN(morning1.id,afternoon1.id) 
          JOIN my_table night1
            ON night1.id NOT IN(morning1.id,afternoon1.id,evening1.id) 
         WHERE morning1.shift = 'morning' 
           AND afternoon1.shift = 'afternoon' 
           AND evening1.shift = 'evening' 
           AND night1.shift = 'night' 
           AND morning1.rate + afternoon1.rate + evening1.rate + night1.rate < 50
           AND LENGTH(REPLACE(CONCAT(morning1.code,afternoon1.code,evening1.code,night1.code),'AA',''))=4
         ORDER
            BY RAND() LIMIT 1;
            
            +----+------+---------+------+----+------+-----------+------+----+------+---------+------+----+------+-------+------+
            | id | code | shift   | rate | id | code | shift     | rate | id | code | shift   | rate | id | code | shift | rate |
            +----+------+---------+------+----+------+-----------+------+----+------+---------+------+----+------+-------+------+
            |  1 | AA   | Morning |   10 | 25 | BB   | Afternoon |    2 | 15 | AA   | Evening |   15 | 27 | BB   | Night |    3 |
            +----+------+---------+------+----+------+-----------+------+----+------+---------+------+----+------+-------+------+

(Един от 721 валидни резултата)