Question

我正在尝试在SQL（在Java程序中）中有效地构造查询以查找历史先决条件＆＃39;适合高中课程。

基本上，我有一个名为PREREQUISITE的表，它由元组（Class_name，Prerequisite_name）组成。然而，一个历史先决条件＆＃39;被定义为所有先决条件，以及所有先决条件的先决条件等等。

当我考虑为每个模块创建一个新表时，使用Java中的深度优先搜索来查找先前的先决条件等，但我认为它的结果非常低效。如果有人能指出如何澄清我的想法，我将非常感激。

如果需要注意的话，我会使用Oracle。

例如，样本数据：

Class_name              Prerequisite_name

EC104                   EC101  
EC106                   EC104  
EC210                   EC106

应提供输出：

EC101:  
EC104: EC101  
EC106: EC101, EC104  
EC210: EC101, EC104, EC106

Answer 1

详细说明RJD的答案，以下是您在Oracle中的方式。

WITH -- PREREQUISITES is just test data that you should have in your table already.. you don't need this part if you have actual tables.
     prerequisites AS
       (SELECT 'EC104' class_name,
               'EC101' prerequisite_name
        FROM   DUAL
        UNION ALL
        SELECT 'EC106',
               'EC104'
        FROM   DUAL
        UNION ALL
        SELECT 'EC210',
               'EC106'
        FROM   DUAL),
     -- CLASSES gets a distinct list of classes, which hopefully you already have in another table.. you don't need this part if you have tables
     classes AS
       (SELECT class_name FROM prerequisites
        UNION
        SELECT prerequisite_name FROM prerequisites),
     -- HIERARCHY gets the historical dependencies -- you need this part
     hierarchy AS
       (SELECT p.*,
               CONNECT_BY_ROOT class_name AS root_class_name
        FROM   prerequisites p
        CONNECT BY class_name = PRIOR prerequisite_name)
SELECT c.class_name,
       LISTAGG (h.prerequisite_name, ',') WITHIN GROUP (ORDER BY h.prerequisite_name)
FROM   classes c LEFT JOIN hierarchy h ON h.root_class_name = c.class_name
GROUP BY c.class_name
ORDER BY c.class_name

Answer 2

在不知道细节的情况下，Oracle是否可能希望查看分层查询。＆＃34; CONNECT BY＆＃34;等

困惑于如何有效地形成此SQL查询

2 个答案: