SQL函数：Group_concat用法

完整语法：

group_concat([DISTINCT] 要连接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])

SELECT * FROM `sqltest`

如果按照group_id分组，会自动去重

SELECT * FROM `sqltest` GROUP BY group_id

 想要类别按组分类集中到一起，就要用Group_concat

SELECT group_id,GROUP_CONCAT(category) FROM `sqltest` GROUP BY group_id

还有几种扩展：

①可以给类别去重

SELECT group_id,GROUP_CONCAT(DISTINCT category) FROM `sqltest` GROUP BY group_id

②给类别排序

SELECT group_id,GROUP_CONCAT(category ORDER BY category DESC) FROM `sqltest` GROUP BY group_id

③给类别更改分隔符

SELECT group_id,GROUP_CONCAT(category SEPARATOR '_') FROM `sqltest` GROUP BY group_id