结果是一样的，用一个简单的例子
第一句
SELECT '姓名' AS 名称, COUNT(*) AS 合计
 FROM mytable
UNION ALL
SELECT name, COUNT(*) AS aa
FROM mytable GROUP BY name

第二句
SELECT '姓名' AS 名称,  sum(aa) AS 合计
FROM (SELECT name,  COUNT(*) AS aa
        FROM mytable   GROUP BY name) AS d
UNION ALL
SELECT name,  COUNT(*) AS aa
FROM mytable GROUP BY name