这篇文章主要介绍“怎么求数据库嵌套表平均值”，在日常操作中，相信很多人在怎么求数据库嵌套表平均值问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”怎么求数据库嵌套表平均值”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
我创建了一个SCHEMA级别的NUMBER型嵌套表：
CREATE OR REPLACE TYPE plch_numbers_t IS TABLE OF NUMBER
/哪些选项实现了一个名字为plch_avg的函数，能够计算一个上述嵌套表中所有元素的平均值，从而使得下列代码块执行之后会显示"3.5"?
DECLARE
l_numbers plch_numbers_t
:= plch_numbers_t (1, 2, 3, 4, 5, 6);
BEGIN
DBMS_OUTPUT.put_line (plch_avg (l_numbers));
END;
/(A)
CREATE OR REPLACE FUNCTION plch_avg (numbers_in IN plch_numbers_t)
RETURN NUMBER
IS
l_index PLS_INTEGER := numbers_in.FIRST;
l_sum NUMBER := 0;
BEGIN
WHILE l_index IS NOT NULL
LOOP
l_sum := l_sum + numbers_in (l_index);
l_index := numbers_in.NEXT (l_index);
END LOOP;
RETURN l_sum / numbers_in.COUNT;
END;
/(B)
CREATE OR REPLACE FUNCTION plch_avg (numbers_in IN plch_numbers_t)
RETURN NUMBER
IS
l_average NUMBER;
BEGIN
SELECT AVG (COLUMN_VALUE) INTO l_average
FROM TABLE (numbers_in);
RETURN l_average;
END;
/(C)
CREATE OR REPLACE FUNCTION plch_avg (numbers_in IN plch_numbers_t)
RETURN NUMBER
IS
BEGIN
RETURN AVG (numbers_in);
END;
/(D)
CREATE OR REPLACE FUNCTION plch_avg (numbers_in IN plch_numbers_t)
RETURN NUMBER
IS
l_index PLS_INTEGER := numbers_in.FIRST;
l_average NUMBER := 0;
BEGIN
WHILE l_index IS NOT NULL
LOOP
l_average := l_average + numbers_in (l_index)/numbers_in.count;
l_index := numbers_in.NEXT (l_index);
END LOOP;
RETURN l_average;
END;
/(E)
CREATE OR REPLACE FUNCTION plch_avg (numbers_in IN plch_numbers_t)
RETURN NUMBER
IS
l_average NUMBER;
BEGIN
SELECT AVG (numbers_in(ROWNUM)) INTO l_average
FROM numbers_in;
RETURN l_average;
END;
/实测答案ABC
C报错 PLS-00204: 函数或伪列 'AVG' 只能在 SQL 语句中使用
E报错 PL/SQL: ORA-00942: 表或视图不存在
答案ABD, B是最佳答案，注意D在某些情况下可能出现误差。
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