如何写一个判断是否在数据库中已经有此记录的存储过程?

Question

CREATE OR REPLACE PROCEDURE PRO_TEST
      (USER_NAME VARCHAR2,
       USER_PWD  VARCHAR2)
AS
      I NUMBER(4);
BEGIN
      SELECT COUNT(*) INTO I 
      FROM TABLE 
      WHERE USERNAME=USER_NAME;
      IF I > 0 THEN
         RAISE_APPLICATION_ERROR(-20007,'數據庫中已經存在'||USER_NAME||'的記錄');
      END IF;
      IF I = 0 THEN
         INSERT INTO TABLE
               (
                USERNAME, 
                PASSWORD
               )
         VALUES(
                USER_NAME,
                USER_PWD
               );
      END IF;
END;