SELECT AR.code_article as a01
, AR.code_client as a02
, (SELECT libelle_client FROM CLIENT CL WHERE CL.code_client = AR.code_client) as a03
FROM ARTICLE
WHERE 1 = 1
GROUP BY a01, a02, (SELECT libelle_client FROM CLIENT CL WHERE CL.code_client = AR.code_client)
With temp as (
SELECT AR.code_article as a01
, AR.code_client as a02
, (SELECT libelle_client FROM CLIENT CL WHERE CL.code_client = AR.code_client) as a03
FROM ARTICLE
WHERE 1 = 1
)
SELECT * FROM temp GROUP BY a01,a02,a03