解决mysql contact 值为空的问题

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#问题描述:
省份城市区域字段有空值,contact 合并为一个值导出,有空值存在.
问题解决:

 DB::raw('CONCAT(IFNULL(service_province,""),IFNULL(service_city,""),IFNULL(service_district,"")) as 服务区域')

添加ifnull判断,添加默认值