在2个不同的表上选择COUNT语句的SUM

Question

我想从不同表上的2个COUNT语句中提取COUNT值。 我试过了：

SELECT(
SELECT COUNT(*) FROM articlegroups 
UNION 
SELECT COUNT(*) FROM emails
) 
as t

我试过了：

SELECT(
SELECT COUNT(*) FROM articlegroups 
+
SELECT COUNT(*) FROM emails
) 
as t

我试过了：

SELECT SUM(
SELECT COUNT(*) FROM articlegroups 
+
SELECT COUNT(*) FROM emails
) 
as t

我不知道还有什么可以尝试...

Answer 1

你没试过：

SELECT SUM(cnt) as cnt FROM
(
    SELECT COUNT(*) as cnt FROM articlegroups 
    UNION ALL
    SELECT COUNT(*) as cnt FROM emails
) t

或者：

SELECT (SELECT COUNT(*) FROM articlegroups) + 
       (SELECT COUNT(*) FROM emails)  as cnt

Answer 2

您可以使用：

SELECT (SELECT COUNT(*) FROM articlegroups) + 
       (SELECT COUNT(*) FROM emails) AS cnt

如果articlegroups或emails可以为空，那么您还应该使用COALESCE：

SELECT COALESCE((SELECT COUNT(*) FROM articlegroups),0) + 
       COALESCE((SELECT COUNT(*) FROM emails),0) AS cnt