[英]Connect by in Oracle SQL
Suppose that we have following tables 假设我们有以下表格
create table Employee(
2 EMPNO NUMBER(3),
3 ENAME VARCHAR2(15 BYTE),
4 HIREDATE DATE,
5 ORIG_SALARY NUMBER(6),
6 CURR_SALARY NUMBER(6),
7 REGION VARCHAR2(1 BYTE),
8 MANAGER_ID NUMBER(3)
9 )
and 和
create table job (
2 EMPNO NUMBER(3),
3 jobtitle VARCHAR2(20 BYTE)
4 )
5 /
I am interested in what the below query does 我对以下查询的作用感兴趣
SELECT empno, manager_id, ename
2 FROM employee
3 START WITH empno = 1
4 CONNECT BY PRIOR empno = manager_id;
As I understood this code selects empno
, manager_id
, ename
from employee, it starts selection from this row where empno=1
, but could not understand what this line does: 据我empno
,这段代码选择了empno
, manager_id
,来自员工的ename
,它从empno=1
这一行开始选择,但无法理解这一行的作用:
CONNECT BY PRIOR empno = manager_id;
Is this the same as: 这是一样的:
where empno=manager_id?
CONNECT BY PRIOR empno = manager_id;
This will produce the recursion. 这将产生递归。 All records that are part of the next lower hierarchical level will return. 将返回属于下一个较低层级的所有记录。 This will return a hierarchy from top to bottom for all managers and their respective under working subordinates. 这将为所有经理及其各自的工作下属返回从上到下的层次结构。
30 (manager_id)
12
5 (manager_id)
1
7
20 (manager_id)
15
10
The query is recursive, it start from employee #1 (CEO probably) and then recursively prints all his subordinates and then all their subordinates and so on and so forth (until all the employees are printed). 该查询是递归的,它从员工#1(可能是CEO)开始,然后递归打印他的所有下属,然后是他们所有的下属,依此类推等等(直到所有员工都被打印出来)。
A good explanation about the "START WITH" and "CONNECT BY" can be found here 关于“START WITH”和“CONNECT BY”的一个很好的解释可以在这里找到
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