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Editorial Team
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Asked: 2026-06-15T00:44:18+00:00

I was hit with the following question today during an interview: How many rows

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I was hit with the following question today during an interview:

How many rows would the following SQL statement return given the two
tables A and B, where both A and B each have exactly 10 rows?:
Select * from A, B;

My answer was the obvious one: 20. However, my interviewer told me that it was allegedly 100, although he said that he didn’t buy that himself. Can anyone shed some light on this?

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1 Answer

  1. Editorial Team

    That query returns a Cartesian product of tables A and B. Every row in table A will be matched with every row in table B. 10 rows * 10 rows = 100 rows.

    You were probably interpreting that as a UNION, where all the rows in table B are appended to the bottom of the rows from table A. That query would look like this:

    SELECT * FROM A
UNION
SELECT * FROM B

    Note that this would only work if the structures of A and B were identical.

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