mysql - 单个查询中来自多个基数的计数

Question

我有 2 个 MySQL 数据库，我想计算每个数据库上两个表中的行数并组合结果。

SELECT count(*) FROM base_1.users;
+----------+
| count(*) |
+----------+
|       15 |
+----------+
SELECT count(*) FROM base_2.users;
+----------+
| count(*) |
+----------+
|       75 |
+----------+

此查询返回第一个计数的结果。

SELECT count(*) FROM base_1.users, base_2.users;
+----------+
| count(*) |
+----------+
|       15 |
+----------+

我可以在单个查询中完成吗？

Answer 1

怎么样

SELECT SUM(c)
FROM 
(
   SELECT count(*) as c FROM base_1.users;
) x
UNION
(
   SELECT count(*) as c FROM base_2.users;
) y

Answer 2

您可以UNION ALL在两个查询之间使用 a ，然后使用SUM()来获取总数：

select sum(total) as TotalCount
from
(
  SELECT count(*) Total
  FROM base_1.users
  UNION ALL
  SELECT count(*) 
  FROM base_2.users
) src