SELECT  (
        SELECT COUNT(*)
        FROM   tbl1
        )
        +
        (
        SELECT COUNT(*)
        FROM   tbl2
        ) 
    as TotalCount

Declare @all int
SET @all = (select COUNT(*) from tab1) + (select count(*) from tab2)
Print @all

or

SELECT (select COUNT(*) from tab1) + (select count(*) from tab2)

SELECT  (
        SELECT COUNT(*)
        FROM   tab1
        ) AS count1,
        (
        SELECT COUNT(*)
        FROM   tab2
        ) AS count2
FROM    dual

    select 
    t1.Count_1,t2.Count_2
    from 
(SELECT count(1) as Count_1 FROM tab1) as t1, 
(SELECT count(1) as Count_2 FROM tab2) as t2

其他略有不同的方法:

with t1_count as (select count(*) c1 from t1),
     t2_count as (select count(*) c2 from t2)
select c1,
       c2
from   t1_count,
       t2_count
/

select c1,
       c2
from   (select count(*) c1 from t1) t1_count,
       (select count(*) c2 from t2) t2_count
/

--============= FIRST WAY (Shows as Multiple Row) ===============
SELECT 'tblProducts' [TableName], COUNT(P.Id) [RowCount] FROM tblProducts P
UNION ALL
SELECT 'tblProductSales' [TableName], COUNT(S.Id) [RowCount] FROM tblProductSales S


--============== SECOND WAY (Shows in a Single Row) =============
SELECT  
(SELECT COUNT(Id) FROM   tblProducts) AS ProductCount,
(SELECT COUNT(Id) FROM   tblProductSales) AS SalesCount