Oracle 中的树查询和 connect by

  • Oracle 中的树查询和 connect by 使用 connect by 和 start with 来建立类似于树的报表并不难,只要遵循以下基本原则即可: 使用 connect by 时各子句的顺序应为: select from where start with connect by order by
  • prior 使报表的顺序为从根到叶(如果 prior 列是父辈)或从叶到根(如果 prior 列是后代)。
  • where 子句可以从树中排除个体,但不排除它们的子孙(或者祖先,如果 prior 列是后代)。
  • connect by 中的条件(尤其是不等于)消除个体和它所有的子孙(或祖先,依赖于怎样跟踪树)。
  • connect by 不能与 where 子句中的表连接在一起使用。

下面是几个例子

1. 从根到叶遍历 SELECT n_parendid, n_name, (LEVEL - 1), n_id FROM navigation WHERE n_parendid IS NOT NULL START WITH n_id = 0 CONNECT BY n_parendid = PRIOR n_id; 2. 从叶到根遍历 SELECT n_parendid, n_name, (LEVEL - 1), n_id FROM navigation WHERE n_parendid IS NOT NULL START WITH n_id = 300 CONNECT BY n_id = PRIOR n_parendid; 3. 排除个体,但不排除它们的子孙 SELECT n_parendid, n_name, (LEVEL - 1), n_id FROM navigation WHERE n_parendid IS NOT NULL AND n_id != 2 START WITH n_id = 0 CONNECT BY n_parendid = PRIOR n_id; 4. 消除个体和它所有的子孙 SELECT n_parendid, n_name, (LEVEL - 1), n_id FROM navigation WHERE n_parendid IS NOT NULL START WITH n_id = 0 CONNECT BY n_parendid = PRIOR n_id AND n_id != 2; 5. 改变显示顺序 SELECT n_parendid, n_name, (LEVEL - 1), n_id FROM navigation WHERE n_parendid IS NOT NULL START WITH n_id = 0 CONNECT BY n_parendid = PRIOR n_id ORDER BY n_viewnum DESC;

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