check if "it's a number" function in Oracle
One additional idea, mentioned here is to use a regular expression to check:
SELECT foo
FROM bar
WHERE REGEXP_LIKE (foo,'^[[:digit:]]+$');
The nice part is you do not need a separate PL/SQL function. The potentially problematic part is that a regular expression may not be the most efficient method for a large number of rows.
Assuming that the ID column in myTable
is not declared as a NUMBER (which seems like an odd choice and likely to be problematic), you can write a function that tries to convert the (presumably VARCHAR2) ID to a number, catches the exception, and returns a 'Y' or an 'N'. Something like
CREATE OR REPLACE FUNCTION is_number( p_str IN VARCHAR2 )
RETURN VARCHAR2 DETERMINISTIC PARALLEL_ENABLE
IS
l_num NUMBER;
BEGIN
l_num := to_number( p_str );
RETURN 'Y';
EXCEPTION
WHEN value_error THEN
RETURN 'N';
END is_number;
You can then embed that call in a query, i.e.
SELECT (CASE WHEN is_number( myTable.id ) = 'Y' AND myTable.id > 0
THEN 'Number > 0'
ELSE 'Something else'
END) some_alias
FROM myTable
Note that although PL/SQL has a boolean data type, SQL does not. So while you can declare a function that returns a boolean, you cannot use such a function in a SQL query.
Saish's answer using REGEXP_LIKE
is the right idea but does not support floating numbers. This one will ...
Return values that are numeric
SELECT foo
FROM bar
WHERE REGEXP_LIKE (foo,'^-?\d+(\.\d+)?$');
Return values not numeric
SELECT foo
FROM bar
WHERE NOT REGEXP_LIKE (foo,'^-?\d+(\.\d+)?$');
You can test your regular expressions themselves till your heart is content at http://regexpal.com/ (but make sure you select the checkbox match at line breaks for this one).