mysql多条相同连接的数据合并一条函数

mysql的函数GROUP_CONCAT，用a.`goods_id` group by开

SELECT a.`goods_id`,GROUP_CONCAT(b.`stock`) FROM t_product a 

LEFT JOIN t_stock_format b 

ON a.`goods_id` = b.`goods_id` 

GROUP BY a.`goods_id`