PL/SQL ORACLE 中的递归函数
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Recursive function in PL/SQL ORACLE
提问by Brijan Elwadhi
In which scenario recursion can be used in PL/SQL
PL/SQL可以在哪些场景下使用递归
CREATE OR REPLACE FUNCTION factorial (
n POSITIVE
) RETURN POSITIVE
IS
BEGIN
IF n = 1 THEN
RETURN n;
ELSE
RETURN n * factorial(n-1);
END IF;
END;
BEGIN
FOR i IN 1..5 LOOP
DBMS_OUTPUT.PUT_LINE(i || '! = ' || factorial(i));
END LOOP;
END;
This will work but I want to know in real world when recursion is required in data base queries
这会起作用，但我想知道在现实世界中何时需要在数据库查询中使用递归
回答by Justin Cave
Depends what you mean by "required". A recursive algorithm can always be rewritten as a loop and a loop can always be rewritten as a recursive algorithm (assuming that the language you're working with supports both loops and function calls). Some algorithms tend to be easier to implement via recursion others tend to be easier to implement via loops.
取决于您所说的“必需”是什么意思。递归算法总是可以重写为循环，而循环总是可以重写为递归算法（假设您使用的语言支持循环和函数调用）。一些算法往往更容易通过递归实现，而另一些算法则更容易通过循环实现。
Using recursion to compute factorials in PL/SQL is a reasonable implementation choice. Using a loop would also be reasonable. If you want to do it in pure SQL rather than resorting to PL/SQL, you could also
在 PL/SQL 中使用递归计算阶乘是一个合理的实现选择。使用循环也是合理的。如果你想用纯 SQL 来做而不是诉诸 PL/SQL，你也可以
select round( exp( sum( ln( level ) ) ) )
from dual
connect by level <= <<some number>>
Which of various reasonable implementations you use depends on a variety of factors-- what approach you're most comfortable with, the speed of the various implementations, etc.
您使用的各种合理实现中的哪一种取决于多种因素——您最熟悉哪种方法、各种实现的速度等。
