Select count(*) from multiple tables

As additional information, to accomplish same thing in SQL Server, you just need to remove the "FROM dual" part of the query.

Just because it's slightly different:

SELECT 'table_1' AS table_name, COUNT(*) FROM table_1
UNION
SELECT 'table_2' AS table_name, COUNT(*) FROM table_2
UNION
SELECT 'table_3' AS table_name, COUNT(*) FROM table_3

It gives the answers transposed (one row per table instead of one column), otherwise I don't think it's much different. I think performance-wise they should be equivalent.

My experience is with SQL Server, but could you do:

select (select count(*) from table1) as count1,
  (select count(*) from table2) as count2

In SQL Server I get the result you are after.

    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

Other slightly different methods:

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
/

A quick stab came up with:

Select (select count(*) from Table1) as Count1, (select count(*) from Table2) as Count2

Note: I tested this in SQL Server, so From Dual is not necessary (hence the discrepancy).

For a bit of completeness - this query will create a query to give you a count of all of the tables for a given owner.

select 
  DECODE(rownum, 1, '', ' UNION ALL ') || 
  'SELECT ''' || table_name || ''' AS TABLE_NAME, COUNT(*) ' ||
  ' FROM ' || table_name  as query_string 
 from all_tables 
where owner = :owner;

The output is something like

SELECT 'TAB1' AS TABLE_NAME, COUNT(*) FROM TAB1
 UNION ALL SELECT 'TAB2' AS TABLE_NAME, COUNT(*) FROM TAB2
 UNION ALL SELECT 'TAB3' AS TABLE_NAME, COUNT(*) FROM TAB3
 UNION ALL SELECT 'TAB4' AS TABLE_NAME, COUNT(*) FROM TAB4

Which you can then run to get your counts. It's just a handy script to have around sometimes.

As I can't see any other answer bring this up.

If you don't like sub-queries and have primary keys in each table you can do this:

select count(distinct tab1.id) as count_t1,
       count(distinct tab2.id) as count_t2
    from tab1, tab2

But performance wise I believe that Quassnoi's solution is better, and the one I would use.

SELECT (SELECT COUNT(*) FROM table1) + (SELECT COUNT(*) FROM table2) FROM dual;

Here is from me to share

Option 1 - counting from same domain from different table

select distinct(select count(*) from domain1.table1) "count1", (select count(*) from domain1.table2) "count2" 
from domain1.table1, domain1.table2;

Option 2 - counting from different domain for same table

select distinct(select count(*) from domain1.table1) "count1", (select count(*) from domain2.table1) "count2" 
from domain1.table1, domain2.table1;

Option 3 - counting from different domain for same table with "union all" to have rows of count

select 'domain 1'"domain", count(*) 
from domain1.table1 
union all 
select 'domain 2', count(*) 
from domain2.table1;

Enjoy the SQL, I always do :)

select (select count(*) from tab1) count_1, (select count(*) from tab2) count_2 from dual;

--============= 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

If the tables (or at least a key column) are of the same type just make the union first and then count.

select count(*) 
  from (select tab1key as key from schema.tab1 
        union all 
        select tab2key as key from schema.tab2
       )

Or take your satement and put another sum() around it.

select sum(amount) from
(
select count(*) amount from schema.tab1 union all select count(*) amount from schema.tab2
)

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

If you're using Google BigQuery this will work.

SELECT
  date,
  SUM(Table_1_Id_Count) AS Table_1_Id_Count,
  SUM(Table_2_Id_Count) AS Table_2_Id_Count
FROM
  (
    SELECT
      Id AS Table_1_Id,
      date,
      COUNT(Id) AS Table_1_Id_Count,
      0 AS Table_2_Id_Count
    FROM
      `your_project_name.Table_1`
    GROUP BY
      Id,
      date
    UNION ALL
    SELECT
      Id AS Table_2_Id,
      date,
      0 AS Table_1_Id_Count,
      COUNT(Id) AS Table_2_Id_Count
    FROM
      `your_project_name.Table_2`
    GROUP BY
      Id,
      date
  )
GROUP BY
  date

You need subqueries:

Select t1.key, t1.col, t2.col, 
    , (Select count(*)
        From table3
        Where key = t1.key) as Count1
    , (Select count(*)
        From table4
        Where key = t1.key) as Count2
From table1 t1
Join table2 t2 on t2.key = t1.key
Where t1.key in (1,2,3)

JOIN with different tables

SELECT COUNT(*) FROM (  
SELECT DISTINCT table_a.ID  FROM table_a JOIN table_c ON table_a.ID  = table_c.ID   );

select (select count() from tab1 where field like 'value') + (select count() from tab2 where field like 'value') count

select @count = sum(data) from
(
select count(*)  as data from #tempregion
union 
select count(*)  as data from #tempmetro
union
select count(*)  as data from #tempcity
union
select count(*)  as data from #tempzips
) a