Question

How can I select count(*) from two different tables (call them tab1 and tab2) having as result:

Count_1   Count_2
123       456

I've tried this:

select count(*) Count_1 from schema.tab1 union all select count(*) Count_2 from schema.tab2

But all I have is:

Count_1
123
456

Answer1

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

Comments

1. why do you need dual? what does that mean?
2. It's a fake table with one record. You can't have SELECT without FROM in Oracle.

Answer2

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

Answer3

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.

Answer4

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.

Answer5

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
/

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