三张表：merchant_area,sys_area,merchant.
SELECT a.id AS "id",
a.merchant_name AS "merchantName",a.merchant_type AS "merchantType",
a.create_time AS "createTime",
a.is_delete AS "isDelete",
c.id AS 'area.id',
c.name AS 'area.name'
FROM merchant a
LEFT JOIN merchant_area b ON b.`merchant_id` = a.`id`
LEFT JOIN sys_area c ON c.`id`=b.`area_id`