仅当为输入参数找到特定元数据时，才会在游标中加入 Oracle JOIN

Question

我有一个像这样连接的游标：

CURSOR C1 IS
SELECT *
        FROM table_1 a
             JOIN table_2 b
                                ON b.ID_1 = a.ID_1
       WHERE     TABLE_ID IS NOT NULL
             AND TABLE_ID = p_input_id;

我想修改游标并仅在元数据 table 中找到 p_input_id 时再添加 3 个连接。所以我想做这样的事情：

CURSOR C1 IS
SELECT *
        FROM table_1 a
             JOIN table_2 b
                                ON b.ID_1 = a.ID_1
             CASE 
                 WHEN EXISTS (SELECT 1 
                              FROM METADATA_TABLE 
                              WHERE INPUT_ID = p_input_id 
                              AND FLAG = 'Y') 
                 THEN 
                     JOIN table_3 c
                                        ON c.ID_2 = b.ID_2
                     JOIN table_4 d
                                        ON d.ID_3 = c.ID_3
             END
       WHERE     TABLE_ID IS NOT NULL
             AND TABLE_ID = p_input_id;

我怎样才能做到这一点？我可以考虑使用 LEFT JOIN 而不是 case/join。这有什么问题吗？

CURSOR C1 IS
SELECT *
        FROM table_1 a
             JOIN table_2 b
                                ON b.ID_1 = a.ID_1
             LEFT JOIN table_3 c
                                ON c.ID_2 = b.ID_2
             LEFT JOIN table_4 d
                                ON d.ID_3 = c.ID_3
       WHERE     TABLE_ID IS NOT NULL
             AND TABLE_ID = p_input_id;

我试图避免破坏正在使用它的 p_input_id 的当前光标。将有新的 p_input_id 需要使用额外的 table 连接。

Answer 1

您可以将 LEFT JOIN 用于 table_3 和 table_4 以及 count 在 metadata table 中，如下所示：

SELECT * FROM TABLE_1 A
    JOIN TABLE_2 B ON B.ID_1 = A.ID_1
    JOIN ( SELECT COUNT(1) AS CNT
             FROM METADATA_TABLE
            WHERE INPUT_ID = P_INPUT_ID
              AND FLAG = 'Y') MT
    LEFT JOIN TABLE_3 C ON C.ID_2 = B.ID_2
                           AND MT.CNT > 0
    JOIN TABLE_4 D ON D.ID_3 = C.ID_3
                      AND MT.CNT > 0
WHERE TABLE_ID IS NOT NULL
  AND TABLE_ID = P_INPUT_ID;

COUNT用于metadatatable保证returns只有一条记录。（替换exists）

仅当为输入参数找到特定元数据时，才会在游标中加入 Oracle JOIN

Oracle JOIN in cursor only if a certain metadata is found for input parameter

sql

oracle

join

oracle18c