DECLARE
l_cnt NUMBER;
BEGIN
SELECT COUNT(*) INTO l_cnt
FROM dba_tab_columns
WHERE owner = 'my_owner'
AND table_name = 'my_table' AND column_name = 'my_column';
IF( l_cnt = 1 ) THEN
EXECUTE IMMEDIATE 'ALTER TABLE my_table DROP COLUMN my_column';
END IF;
END;