PLSQL - 利用Object Type实现Greatest/Least忽略空值计算
之前发布过利用自定义函数实现greatest和least忽略空值计算的文章，最近又想到可以用对象类型来实现，不算成熟，抛砖引玉。
本例以最多容纳五个数字入参为例：
CREATE OR REPLACE TYPE bhsc_numeric_battle AS OBJECT
(
-- 输入属性
num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER,
num4 NUMBER,
-- 比较结果，作为属性只是为了方便应用，并不允许输入
greatest NUMBER,
least NUMBER,
-- 用于比较入参的过程，不需要调用
MEMBER PROCEDURE battle,
-- 自定义构造函数，用于支持不定量入参
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER)
RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER)
RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER)
RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER)
RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER,
num4 NUMBER)
RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER,
num4 NUMBER,
greatest NUMBER)
RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER,
num4 NUMBER,
greatest NUMBER,
least NUMBER)
RETURN SELF AS RESULT
)
/
CREATE OR REPLACE TYPE BODY bhsc_numeric_battle IS
-- 该过程用于比较计算出两个最值，在实例化时内部调用，无需用户调用
MEMBER PROCEDURE battle IS
BEGIN
greatest := coalesce(num0, num1, num2, num3, num4);
least := coalesce(num4, num3, num2, num1, num0);
IF greatest IS NULL THEN
RETURN;
END IF;
IF least > greatest THEN
SELECT least, greatest INTO greatest, least FROM dual;
END IF;
IF num0 > greatest THEN
greatest := num0;
ELSIF num0 < least THEN
least := num0;
END IF;
IF num1 > greatest THEN
greatest := num1;
ELSIF num1 < least THEN
least := num1;
END IF;
IF num2 > greatest THEN
greatest := num2;
ELSIF num2 < least THEN
least := num2;
END IF;
IF num3 > greatest THEN
greatest := num3;
ELSIF num3 < least THEN
least := num3;
END IF;
IF num4 > greatest THEN
greatest := num4;
ELSIF num4 < least THEN
least := num4;
END IF;
END;
-- 这两个构造函数专门用于禁止用户实例化greatest和least
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER,
num4 NUMBER,
greatest NUMBER)
RETURN SELF AS RESULT IS
too_many_arguments EXCEPTION;
PRAGMA EXCEPTION_INIT(too_many_arguments, -909);
BEGIN
RAISE too_many_arguments;
END bhsc_numeric_battle;
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER,
num4 NUMBER,
greatest NUMBER,
least NUMBER)
RETURN SELF AS RESULT IS
too_many_arguments EXCEPTION;
PRAGMA EXCEPTION_INIT(too_many_arguments, -909);
BEGIN
RAISE too_many_arguments;
END bhsc_numeric_battle;
-- 这些构造函数用于支持不定量入参，给未输入的属性赋予空值，并调用battle计算最值
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER) RETURN SELF AS RESULT IS
BEGIN
self.num0 := num0;
self.num1 := NULL;
self.num2 := NULL;
self.num3 := NULL;
self.num4 := NULL;
battle;
RETURN;
END bhsc_numeric_battle;
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER) RETURN SELF AS RESULT IS
BEGIN
self.num0 := num0;
self.num1 := num1;
self.num2 := NULL;
self.num3 := NULL;
self.num4 := NULL;
battle;
RETURN;
END bhsc_numeric_battle;
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER) RETURN SELF AS RESULT IS
BEGIN
self.num0 := num0;
self.num1 := num1;
self.num2 := num2;
self.num3 := NULL;
self.num4 := NULL;
battle;
RETURN;
END bhsc_numeric_battle;
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER) RETURN SELF AS RESULT IS
BEGIN
self.num0 := num0;
self.num1 := num1;
self.num2 := num2;
self.num3 := num3;
self.num4 := NULL;
battle;
RETURN;
END bhsc_numeric_battle;
CONSTRUCTOR FUNCTION bhsc_numeric_battle(num0 NUMBER,
num1 NUMBER,
num2 NUMBER,
num3 NUMBER,
num4 NUMBER) RETURN SELF AS RESULT IS
BEGIN
self.num0 := num0;
self.num1 := num1;
self.num2 := num2;
self.num3 := num3;
self.num4 := num4;
battle;
RETURN;
END bhsc_numeric_battle;
END;
/
在使用的时候，对象被实例化出来的同时，其greatest和least属性便已计算好，并可在游标中直接引用了。
例如有这样一张表：
SQL> SELECT * FROM bhsc_numeric_battle_demo;
ROWSEQ NUM0 NUM1 NUM2 NUM3 NUM4
---------- ---------- ---------- ---------- ---------- ----------
1 -23.49 -26.91
2 -40.78 -33.19 63.89 -52.48 18.52
3 99.12
4
5 56.85 71.81 41.41 31.09可在SQL中直接得到它五列中的最值：
SELECT rowseq, bhsc_numeric_battle(num0, num1, num2, num3, num4) x
FROM bhsc_numeric_battle_demo;
或者也可以只比较后三列：
SELECT rowseq, bhsc_numeric_battle(num2, num3, num4) x
FROM bhsc_numeric_battle_demo;
但是不要输入超过五个值：
SQL> SELECT bhsc_numeric_battle(1, 2, 3, 4, 5, 6) x FROM dual;
SELECT bhsc_numeric_battle(1, 2, 3, 4, 5, 6) x FROM dual
ORA-00909: 参数个数无效
ORA-06512: 在 "APPS.BHSC_NUMERIC_BATTLE", line 55