Question

I have four related tables and, using the following query, combine them with 4 LEFT JOIN and 2 MAX() aggregate functions:

SELECT SQL_CALC_FOUND_ROWS
         id,
         cognome,
         nome,
         sesso,
         pr_sedute_complessive,
         presa_in_carico_data,
         cf,
         cnome,
         tdr_cognome,
         tdr_nome,
         COUNT(tbl_trattamenti.trt_id),
         MAX(tbl_trattamenti.data),
         pr_id
FROM     tbl_aziente p1
  LEFT JOIN comuni
         ON comuni.cid = p1.nascita_luogo 
  LEFT JOIN tbl_cartellaclinica
         ON tbl_cartellaclinica.pz_fk_id = p1.id 
  LEFT JOIN tbl_progetto
         ON tbl_progetto.cc_id_fk = tbl_cartellaclinica.cc_id 
  LEFT JOIN tbl_fisioterapista
         ON tbl_fisioterapista.tdr_id = tbl_progetto.pr_fisioterapista_fk 
  LEFT JOIN tbl_trattamenti
         ON tbl_progetto.pr_id = tbl_trattamenti.pr_fk_id 
WHERE    idoneo = 'y'
     AND p1.tipo_assistenza = 4
GROUP BY p1.id
LIMIT 0, 10

This is all okay, except for one thing: I want the record from tbl_progetto which has the highest id rather than the first. I’ve tried to use MAX(primaryKey), but I then get only the key – not the record having that pKey.

Answer 1

The basic principle is that you need to reference tbl_progetto twice – once in a subquery that identifies the id of the records of interest, and a second time to fetch the rest of that record.

Assuming that there is a many-to-one relationship between tbl_cartellaclinica and tbl_progetto, the subquery would be:

SELECT   tbl_cartellaclinica.pz_fk_id, MAX(tbl_progetto.pr_id) AS pr_id
FROM     tbl_cartellaclinica
    JOIN tbl_progetto
      ON tbl_progetto.cc_id_fk = tbl_cartellaclinica.cc_id
GROUP BY tbl_cartellaclinica.pz_fk_id

And therefore your modified query would be:

SELECT SQL_CALC_FOUND_ROWS
         id,
         cognome,
         nome,
         sesso,
         pr_sedute_complessive,
         presa_in_carico_data,
         cf,
         cnome,
         tdr_cognome,
         tdr_nome,
         COUNT(tbl_trattamenti.trt_id),
         MAX(tbl_trattamenti.data),
         t.pr_id
FROM     tbl_aziente p1
  LEFT JOIN comuni
         ON comuni.cid = p1.nascita_luogo 
  LEFT JOIN tbl_cartellaclinica
         ON tbl_cartellaclinica.pz_fk_id = p1.id
  LEFT JOIN (
    SELECT   tbl_cartellaclinica.pz_fk_id, MAX(tbl_progetto.pr_id) AS pr_id
    FROM     tbl_cartellaclinica
        JOIN tbl_progetto
          ON tbl_progetto.cc_id_fk = tbl_cartellaclinica.cc_id
    GROUP BY tbl_cartellaclinica.pz_fk_id
  ) AS t ON t.pz_fk_id = tbl_cartellaclinica.pz_fk_id
  LEFT JOIN tbl_progetto
         ON tbl_progetto.cc_id_fk = tbl_cartellaclinica.cc_id
        AND tbl_progetto.pr_id = t.pr_id
  LEFT JOIN tbl_fisioterapista
         ON tbl_fisioterapista.tdr_id = tbl_progetto.pr_fisioterapista_fk 
  LEFT JOIN tbl_trattamenti
         ON tbl_progetto.pr_id = tbl_trattamenti.pr_fk_id 
WHERE    idoneo = 'y'
     AND p1.tipo_assistenza = 4
GROUP BY p1.id
LIMIT    0, 10