check if “it's a number” function in Oracle

Question

I\'m trying to check if a value from a column in an oracle (10g) query is a number in order to compare it. Something like:

select case when ( is_number(myTab         


        

Answer 1

Assuming that the ID column in myTable is not declared as a NUMBER (which seems like an odd choice and likely to be problematic), you can write a function that tries to convert the (presumably VARCHAR2) ID to a number, catches the exception, and returns a 'Y' or an 'N'. Something like

CREATE OR REPLACE FUNCTION is_number( p_str IN VARCHAR2 )
  RETURN VARCHAR2 DETERMINISTIC PARALLEL_ENABLE
IS
  l_num NUMBER;
BEGIN
  l_num := to_number( p_str );
  RETURN 'Y';
EXCEPTION
  WHEN value_error THEN
    RETURN 'N';
END is_number;

You can then embed that call in a query, i.e.

SELECT (CASE WHEN is_number( myTable.id ) = 'Y' AND myTable.id > 0 
               THEN 'Number > 0'
             ELSE 'Something else'
         END) some_alias
  FROM myTable

Note that although PL/SQL has a boolean data type, SQL does not. So while you can declare a function that returns a boolean, you cannot use such a function in a SQL query.