背景:DataEase饼图有特定格式，并且报表要求全部使用SQL语句获取数据
原先数据格式如下，需要行转换列
转换后结果：
原理
字段1，target作为一个不存在的字段，用于命名。
字段2，count字段是关键，将查询结果命名为统一名称，实现行转列。
UNION 拼接三句一样的SQL语句
更改后SQL
( SELECT "车位总数" AS 'target', total_num AS "count" FROM park_free_space_num ORDER BY report_time DESC LIMIT 1 ) UNION
( SELECT "已使用车位" AS 'target', (total_num - free_space_num) AS "count" FROM park_free_space_num ORDER BY report_time DESC LIMIT 1 ) UNION
(SELECT"剩余车位" AS 'target',free_space_num AS "count" FROMpark_free_space_num ORDER BYreport_time DESC LIMIT 1 )
