添加几个COUNT个查询的结果

Question

我试图在一个查询中获取几个计数的总和：

SELECT(
    SELECT COUNT( * )
    FROM comments +
    SELECT COUNT( * )
    FROM tags +
    SELECT COUNT( * )
    FROM search
)

我在这里遗漏了一些东西。我收到语法错误。

Answer 1

SELECT ( SELECT COUNT(*) FROM comments ) 
     + ( SELECT COUNT(*) FROM tags ) 
     + ( SELECT COUNT(*) FROM search )

Answer 2

还有一个（不确定是否支持MySQL，但是 - 在SQL Server中有效）：

SELECT SUM(Counts) FROM
  (SELECT COUNT(*) AS Counts FROM COMMENTS UNION ALL
   SELECT COUNT(*) FROM Tags UNION ALL
   SELECT COUNT(*) FROM Search) s

Answer 3

SELECT (
       SELECT  COUNT(*)
       FROM    comments
       ) +
       (
       SELECT  COUNT(*)
       FROM    tags
       ) +
       (
       SELECT  COUNT(*)
       FROM    search
       )

Answer 4

SELECT SUM(ThisCount)
  FROM (
    SELECT COUNT(*) AS ThisCount
      FROM comments

    UNION ALL

    SELECT COUNT(*) AS ThisCount
      FROM tags

    UNION ALL

    SELECT COUNT(*) AS ThisCount
      FROM search
    )