Question

I have a table Calculators and I want to create an SQL query that returns a boolean result, true if and only if Calculators is not empty so I can return this boolean to my application and order more.

The natural thing would be to use

EXISTS Calculators

But for my assignment, I’m not allowed to use either the EXISTS keyword or the COUNT keyword (or any other cardinality operators) in any of my queries.

My best attempt at a query to perform this so far is

((SELECT * FROM Calculators) IN ANY (SELECT * FROM Calculators))

But this just gives a syntax error that I can’t figure out.

I had another attempt:

((SELECT * FROM Calculators) IN Calculators)

But this also gives a syntax error? I really think this can be done using IN somehow, but I can’t quite form the query. Can you help me get a boolean from my query that returns true if Calculators is non-empty?

Thank you!

Answer 1

I’m confused by your question. You want to return a boolean result if your table is not empty? If so, something like this should work:

SELECT DISTINCT 'True' RetVal FROM Calculators

Sample SQL Fiddle

This will return a single boolean True value if any records exist. It won’t return anything if no records exist. Don’t think you can return false without using COUNT or some other aggregate. Might depend on your RDBMS.

–EDIT–

Seeing that you’re using Oracle, here is a hack to return true or false:

SELECT DISTINCT 'True' RetVal
FROM Calculators
UNION 
SELECT 'False' FROM DUAL d
LEFT JOIN Calculators c ON 1=1
WHERE CalculatorId IS NULL

And more fiddle.