某列 字段 所屬模糊不清

例子：

SELECTa.class_id AS "classInfo.id",                 ci.class_name AS "classInfo.className"FROM class_student_info aLEFT JOIN class_info ci ON a.class_id = ci.class_idWHEREis_valid=0 此處應說明該字段 是哪張表的

               and a.student_id = '1'

改為：

SELECTa.class_id AS "classInfo.id",                ci.class_name AS "classInfo.className"FROM class_student_info aLEFT JOIN class_info ci ON a.class_id = ci.class_idWHEREa.is_valid=0       and a.student_id = '1'