Creating Procedures
The following is a code sample that will create a stored procedure named PROC_RESET_ERROR_LOG:
CREATE PROCEDURE PROC_RESET_ERROR_LOG IS
BEGIN
  — Clean out the ERRORS table
  DELETE FROM ERRORS;
  COMMIT;
END;

The syntax to create a function is similar to the syntax used to create a procedure, with one addition: the RETURN declaration. The following is a sample CREATE FUNCTION statement.
CREATE OR REPLACE FUNCTION FUNC_COUNT_GUESTS
  (p_cruise_id NUMBER)
RETURN NUMBER
IS

  v_count NUMBER(10)
BEGIN
  SELECT COUNT(G.GUEST_ID)
  INTO   v_count
FROM     GUESTS G,
         GUEST_BOOKINGS GB
WHERE    G.GUEST_ID = GB.GUEST_BOOKING_ID
  AND    GB.CRUISE_ID = p_cruise_id;
RETURN   v_count;
END;

This function will take a single parameter, p_cruise_id. This parameter could include the parameter type declaration, such as IN, OUT, or IN OUT, but this example leaves it out, so this parameter is assumed to be the default IN parameter type, just as it would be assumed in a procedure. This function will use the p_cruise_id parameter to query the database and count the total number of guests for a single cruise. The result of the query is then returned to the calling block, using the RETURN statement at the end of the function.
If you think of the entire function as a variable, then think of the RETURN datatype as the function’s datatype.

Altering Procedures
Once a procedure has been created, you can use two methods to “alter” the procedure. If you are replacing the original source code with a new set of source code, use the OR REPLACE option discussed in the previous section. This is true for any code modification at all. If, however, you are recompiling the procedure without changing the code, then use the ALTER PROCEDURE command.
The ALTER PROCEDURE command is required when your stored procedure has not been changed in and of itself, but another database object referenced from within your procedure, such as a table, has been changed. This automatically causes your procedure to be flagged as INVALID.
CREATE OR REPLACE PROCEDURE PROC_RESET_ERROR_LOG IS
BEGIN
  — Clean out the ERRORS table
  DELETE FROM ERRORS;
  COMMIT;
END;

ALTER PROCEDURE PROC_RESET_ERROR_LOG COMPILE;
As with a procedure, a function may reference database objects from within its code. As with a procedure, if those database objects are changed, then the function must be recompiled. To perform this recompilation, use the ALTER FUNCTION COMPILE command.
ALTER FUNCTION FUNC_COUNT_GUESTS COMPILE;
CREATE OR REPLACE FUNCTION FUNC_COUNT_GUESTS
  (p_cruise_id NUMBER)
RETURN NUMBER
IS
  v_count NUMBER(10)
BEGIN
  Statements;
END;
Dropping Procedures
An example of a command that drops a procedure is shown in the following code listing:
DROP PROCEDURE PROC_RESET_ERROR_LOG;
Once this command is successfully executed, the database response “Procedure dropped” will be displayed.
To drop a function, use the DROP … FUNCTION statement. The following is a sample command that will drop our sample function:
DROP FUNCTION FUNC_COUNT_GUESTS;

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