WHERe子句一次只能查看一行中的列。
因此，如果您需要一个条件应用于表中的两个 不同 行，则需要两次连接到该表，以便可以从这两个行中获取列。
SELECt p.*FROM "products" AS pINNER JOIN "custom_field_answers" AS a1 ON p."id" = a1."product_id"INNER JOIN "custom_field_answers" AS a2 ON p."id" = a1."product_id" WHERe a1."value" = 'bangle' AND a2."number_value" < 50
