在同一个 table 上插入 select 语句

Question

我目前正在将数据从遗留系统迁移到当前系统。

我在存储过程中有这个 INSERT 语句。

INSERT INTO TABLE_1
(PRIMARY_ID, SEQUENCE_ID, DESCR)
SELECT LEGACY_ID PRIMARY_ID
 , (SELECT COUNT(*) + 1
    FROM TABLE_1 T1
    WHERE T1.PRIMARY_ID = L1.LEGACY_ID) SEQUENCE_ID
 , L1.DESCR
FROM LEGACY_TABLE L1;

但是，每当我有来自 LEGACY_TABLE 的多个 LEGACY_ID 值时，对 SEQUENCE_ID 的查询不会递增。

为什么会这样？我似乎找不到任何关于 INSERT INTO SELECT 语句在幕后如何工作的文档。我猜它会从您选择的 table 中选择所有值，然后同时插入它们，这就是为什么它不会增加 COUNT(*) 值？

我还能采取哪些其他解决方法？我无法创建 SEQUENCE，因为 SEQUENCE_ID 必须基于存在的 PRIMARY_ID 的数量。它们都是主 ID。

提前致谢。

Answer 1

是的，SELECT 将被执行 FIRST 然后 INSERT 才会发生。

下面的简单 PL/SQL 块将是一种更简单的方法，但效率不高。

DECLARE
    V_SEQUENCE_ID NUMBER;
    V_COMMIT_LIMIT:= 20000;
    V_ITEM_COUNT := 0;
BEGIN
    FOR REC IN (SELECT LEGACY_ID,DESCR FROM LEGACY_TABLE)
    LOOP
        V_SEQUENCE_ID:= 0;

        SELECT COUNT(*)+1 INTO V_SEQUENCE_ID FROM TABLE_1 T1
         WHERE T1.PRIMARY_ID = REC.LEGACY_ID


        INSERT INTO TABLE_1
        (PRIMARY_ID, SEQUENCE_ID, DESCR)
        VALUES
        (REC.LEGACY_ID,V_SEQUENCE_ID,REC.DESCR);

        V_ITEM_COUNT := V_ITEM_COUNT + 1;

        IF(V_ITEM_COUNT >= V_COMMIT_LIMIT)
        THEN
             COMMIT;
             V_ITEM_COUNT := 0;
        END IF;

    END LOOP;
    COMMIT;
END;
/

EDIT: Using CTE:

WITH TABLE_1_PRIM_CT(PRIMARY_ID, SEQUENCE_ID) AS
(
    SELECT L1.LEGACY_ID,COUNT(*) 
    FROM LEGACY_TABLE L1 
      LEFT OUTER JOIN TABLE_1 T1 
        ON(L1.LEGACY_ID = T1.PRIMARY_ID)
    GROUP BY L1.LEGACY_ID
)
INSERT INTO TABLE_1
(SELECT L1.LEGACY_ID,
       CTE.SEQUENCE_ID+ (ROW_NUMBER() OVER (PARTITION BY L1.LEGACY_ID ORDER BY null)), 
       L1.DESCR
FROM TABLE_1_PRIM_CT CTE, LEGACY_TABLE L1
WHERE L1.LEGACY_ID = CTE.PRIMARY_ID);

PS: With your Millions of Rows, this is going to create a temp table of same size, during execution. Do Explain Plan before actual execution.

在同一个 table 上插入 select 语句

Insert into select statement on the same table

oracle

plsql

oracle-sqldeveloper

oracle11gr2