Question

我正在尝试从表中获取记录。我的表结构如下，“ id”是主键

| id | location| parent_id |
|----|---------|-----------|
| 1  | abc     | NULL      |
| 2  | xyz     | 1         | 
| 3  | def     | 2         |

我正在尝试获取ID，名称，parent_id和parent_name。我正在使用下面的联接查询来获取结果，并且工作正常。我只是想发表意见，是否有更好的方法来获得结果。

我已经使用联接查询来获取结果。

SELECT location1.id as childid,
location1.location as childlocation ,
locationparent.id as parentid,
locationparent.location as parentlocation  
FROM location  location1
JOIN location  locationparent 
ON location1.parent_id = locationparent.id  
WHERE location1.id =2  ;

Answer 1

这里是一个示例，说明如何通过分层查询（使用CONNECT BY）实现此目的。我添加了一些示例数据行，以更好地演示这一概念。

SQL> WITH location_tbl (id, location, parent_id) AS (
  2    SELECT 1, 'abc', NULL from dual UNION ALL
  3    SELECT 2, 'xyz', 1 from dual UNION ALL
  4    SELECT 3, 'def', 2 from dual UNION ALL
  5    SELECT 4, 'ggg', 2 from dual UNION ALL
  6    SELECT 5, 'hhh', 3 from dual UNION ALL
  7    SELECT 6, 'iii', 3 from dual
  8  )
  9  SELECT id, location, parent_id, PRIOR location parent_location
 10    FROM location_tbl
 11    CONNECT BY PRIOR id = parent_id
 12    START WITH id = 1;

        ID LOCATION  PARENT_ID PARENT_LOCATION
---------- -------- ---------- ---------------
         1 abc                                
         2 xyz               1 abc            
         3 def               2 xyz            
         5 hhh               3 def            
         6 iii               3 def            
         4 ggg               2 xyz

从表中获取值的正确方法

1 个答案: