SELECT "TablaA."."Campo1", "TablaB."."Campo1", "TablaC."."Campo1"
FROM "TablaA"
LEFT OUTER JOIN "TablaB" ON (("TablaA"."idDocumento" = "TablaB"."idDocumento"))
LEFT OUTER JOIN "TablaC" ON (("TablaA"."idDocumento" = "TablaC"."idDocumento"))
where "TablaA"."Flag" in ('B', 'C')