同一查询上有两个单独的联接

Question

I have a query to find duplicates in a table:

SELECT sofferenze.id_soff, sofferenze.Descrizione
FROM sofferenze
INNER JOIN (
SELECT Descrizione
FROM sofferenze
GROUP BY Descrizione
HAVING count( id ) >1
)dup ON sofferenze.Descrizione = dup.Descrizione
ORDER BY Descrizione ASC

It works like a charm and gives me all the duplicated rows. I also have another query that starting from sofferenze.id_soff will give me another value in another table:

SELECT cod_fisc
FROM anagrafiche
JOIN `rischiatura` ON anagrafiche.id_ndg = rischiatura.id_ndg
WHERE id_ogg = 'SF000000012'
AND id_ruolo = 'RU010000002'

Actually this second query is run for each row returned by the first query replacing in this line WHERE id_ogg='SF000000012' the value 'SF000000012' with the value sofferenze.id_soff that is returned by the first query.

This code is not efficient because it runs several times the second query. Are there any option that I can merge the two queries?

Answer 1

Why not combine it into a sub-query?

SELECT cod_fisc
FROM anagrafiche
JOIN `rischiatura` ON anagrafiche.id_ndg = rischiatura.id_ndg
WHERE id_ogg IN (SELECT x.id_soff
    FROM sofferenze x
    WHERE x.Descrizione IN (
        SELECT ix.Descrizione
        FROM sofferenze ix
        GROUP BY ix.Descrizione
        HAVING count( * ) >1
    ))
AND id_ruolo = 'RU010000002'