PL/SQL custom function FUNCTION

1. Functions are divided into built-in functions and custom functions

-- Custom function FUNCTION 

CREATE OR REPLACE FUNCTION 函数名 (形参1 数据类型1,形参2 数据类型2)
RETURN 返回数据类型
IS / AS 
-- 声明变量的地方

BEGIN
  函数的具体逻辑
  RETURN 声明变量 -- 里面必须要有一个 RETURN 的 字句

END;

-- General naming convention 
-- variables are represented by V_ 
-- parameters are represented by P_
-- custom functions FUN_

 --Define a function, input a number, and calculate the cumulative value from 1 to that number.

CREATE OR REPLACE FUNCTION FUN_SUM(P_SUM NUMBER)
RETURN NUMBER
IS 
V_SUM NUMBER:=0;

BEGIN
  FOR X IN 1..P_SUM LOOP
    V_SUM:=V_SUM + X;
    END LOOP;
    RETURN V_SUM;
END;

-- Query statement call

SELECT 
FUN_SUM(1000)
FROM DUAL;

-- Anonymous code block, call

DECLARE 
P_SUM NUMBER:=&INPUT;
BEGIN
DBMS_OUTPUT.put_line(FUN_SUM(P_SUM));
END;