如何在 Oracle 中编写带循环的查询

Question

如何编写一个循环执行以下任务的查询： （代入个别结果的id）

    SELECT * From Table where id= 24
    Id | next_to_check  |  next_to_check_2
     24|    34,23       | 4

然后我们检查我们显示的意思是 34,23,4

    SELECT * From tablle where id = 34
    SELECT * From tablle where id = 23
    SELECT * From tablle where id = 4

然后用结果替换结果 34,23,4 然后结果越来越深

24-> 34,23,4
34-> which results in a
23-> which results in a
4-> is as a result of

什么结果 -> 结果与结果等等......

当我手动执行时，它看起来像这样：

Answer 1

如果表已正确规范化，查询将非常简单。
正如cmets中提到的，有两个问题：

• next_to_check 和 next_to_check2 是存储相同值的两列
• 两列都包含用逗号分隔的值列表，而不是单个值

表格应如下所示：

SELECT * From Table where id= 24
    Id | next_to_check  | 
     24|    34          | 
     24|    23          |
     24|    4           |

其中next_to_check 列的类型必须与id 列相同，以避免不必要的强制转换。

对于上表，查询可能只是：

SELECT *
FROM "TABLE"
start with id = 24
connect by id = prior next_to_check;

---

如果无法对表进行规范化，则可以使用如下查询“即时”规范化数据：

WITH normalized_data As (
    SELECT id, trim(regexp_substr(next_to_check, '[^,]+', 1, LEVEL)) next_to_check
    FROM "TABLE"
    CONNECT BY LEVEL <= regexp_count(next_to_check, ',')+1  
    UNION ALL
    SELECT id, trim(regexp_substr(next_to_check_2, '[^,]+', 1, LEVEL)) next_to_check
    FROM "TABLE"
    CONNECT BY LEVEL <= regexp_count(next_to_check_2, ',')+1 
)
SELECT * FROM normalized_data

然后将第一个查询粘合到上面的查询：

WITH normalized_data As (
    SELECT id, trim(regexp_substr(next_to_check, '[^,]+', 1, LEVEL)) next_to_check
    FROM "TABLE"
    CONNECT BY LEVEL <= regexp_count(next_to_check, ',')+1  
    UNION ALL
    SELECT id, trim(regexp_substr(next_to_check_2, '[^,]+', 1, LEVEL)) next_to_check
    FROM "TABLE"
    CONNECT BY LEVEL <= regexp_count(next_to_check_2, ',')+1 
)
SELECT * FROM normalized_data
start with id = 24
connect by id = prior next_to_check;

但是这种“解决方法”的性能会很差，它可能适用于 100 或 1000 条记录，但在更大的表上需要数年时间。