DB2 Use select count(*) in fetch first

Question

How can I use Select Count(*) in Fetch First
or will be another way to limit the result length.

Table A

PK
1

Table B

PK
1
2

WITH ALL_DATA AS
    (SELECT *
     FROM TABLE_A
    )
    SELECT *
    FROM TABLE B
    FETCH FIRST (SELECT COUNT(*) FROM WITH ALL_DATA) ROWS ONLY
    )

I am expecting the first row with item 1 from Table B. I am using DB2 LUW.

Answer 1

The syntax could be slightly different.
You may enumerate the B rows first and use their number in the WHERE clause.

WITH ALL_DATA AS
    (SELECT *
     FROM (VALUES 1, 2) A (I)
    )
SELECT I
FROM 
(
    SELECT B.*, ROW_NUMBER () OVER () AS RN_
    FROM (VALUES 1, 2, 3) B (I)
)
WHERE RN_ <= (SELECT COUNT(*) FROM ALL_DATA)

I
1
2

fiddle