mysql 使用 CONCAT、GROUP_CONCAT 嵌套查询出 json 格式数据

tb_factory表由 factory_code 和 factory_name 字段，查询出如下所示效果：

{
    "factory_0001": "工厂1",
    "factory_0002": "工厂2",
    ...
}

select sql：

SELECT 
	CONCAT( 
		"{",
		GROUP_CONCAT( CONCAT( 
					CONCAT( "\"",factory_code,"\"" ),
					":",
					CONCAT( "\"",factory_name,"\"" )
			             ) SEPARATOR ',' ),
		"}"
	      ) AS factory_codes
FROM 
	tb_factory