Query blocking entirely MySQL server - mysql

Question

I try to a run a specific query. However, when I execute it, the MySQL server doesn't respond anymore.
There is approximately 30000 rows in the table base_contrats_actifs but I don't know if this is a problem.
Here is the query :
UPDATE
base_contrats_actifs a
SET
a.code_indice = (
SELECT
MAX(g.code_indice)
FROM
base_gid g
WHERE
a.num_version = g.num_version_contrat
),
a.flag_bailleur_locataire = (
SELECT
MAX(g.flag_bailleur_locataire)
FROM
base_gid g
WHERE
a.num_version = g.num_version_contrat
),
a.compte_client = (
SELECT
MAX(g.compte_client)
FROM
base_gid g
WHERE
a.num_version = g.num_version_contrat
)
Can you see if there is an error ? If not, is there any way to debug the query ?

Answer 1

I don't know exactly why your update is non performant, but given the number of correlated subqueries you have, I'm not surprised. Try rewriting it as an update join:
UPDATE base_contrats_actifs a
INNER JOIN
(
SELECT
num_version_contrat,
MAX(code_indice) AS max_code_indice,
MAX(flag_bailleur_locataire) AS max_flag_bailleur_locataire,
MAX(compte_client) AS max_compte_client
FROM base_gid
GROUP BY num_version_contrat
) g
ON a.num_version = g.num_version_contrat
SET
a.code_indice = g.max_code_indice,
a.flag_bailleur_locataire = g.max_flag_bailleur_locataire,
a.compte_client = g.max_compte_client;