ORACLE - Select Count on a Subquery

Question

I\'ve got an Oracle table that holds a set of ranges (RangeA and RangeB). These columns are varchar as they can hold both numeric and alphanumeric values, like the following exa

Answer 1

You can test each column with a regular expression to determine if it is a valid number:

SELECT COUNT(1)
FROM   table_of_ranges
WHERE  CASE WHEN REGEXP_LIKE( RangeA, '^-?\d+(\.\d*)?$' )
            THEN TO_NUMBER( RangeA )
            ELSE NULL END
          < 10
AND    REGEXP_LIKE( RangeB, '^-?\d+(\.\d*)?$' );

Another alternative is to use a user-defined function:

CREATE OR REPLACE FUNCTION test_Number (
  str VARCHAR2
) RETURN NUMBER DETERMINISTIC
AS
  invalid_number EXCEPTION;
  PRAGMA EXCEPTION_INIT(invalid_number, -6502);
BEGIN
  RETURN TO_NUMBER( str );
EXCEPTION
  WHEN invalid_number THEN
    RETURN NULL;
END test_Number;
/

Then you can do:

SELECT COUNT(*)
FROM   table_of_ranges
WHERE  test_number( RangeA ) <= 10
AND    test_number( RangeB ) IS NOT NULL;