Oracle 别这样

如果你有像这样的更新

UPDATE MAIN_TBL MT
SET MT.STOP_FLAG = (  
    SELECT 
        CASE 
            WHEN {whatever condition}
            THEN 'SF01'
            ELSE MT.STOP_FLAG
        END
    FROM DUAL
)

UPDATE MAIN_TBL MT
SET MT.STOP_FLAG = (  
    SELECT 
        CASE 
            WHEN {whatever condition}
            THEN 'SF01'
            ELSE MT.STOP_FLAG
        END
    FROM DUAL
)

那基本上是一样的

UPDATE MAIN_TBL MT
SET MT.STOP_FLAG = 'SF01'
WHERE {whatever condition}

下面的示例很可能不是一个有效的解决方案，但它们应该给您一个提示，说明如何更好地编写此类更新

UPDATE MAIN_TBL MT
SET
    MT.STOP_FLAG = 'SF01',
    MT.ES = 'E',
    MT.PW = 'W'
    MT.UPDATE_DT = SYSDATE
WHERE 
    MT.STOP_FLAG IS NULL
    AND MT.IDX_2 = 'G'
    AND MT.ES IS NULL
    AND MT.SS = 'C'
    AND MT.PW = 'A'
    AND NOT EXISTS (
        SELECT 1 
        FROM LARGE_TBL LT 
        WHERE LT.LT_ID = MT.MT_ID 
           AND (LT.IDX_2 = 'G' OR LT.COL_1 <> 'Y' OR LT.COL_1 IS NULL)
        );


UPDATE 
    (SELECT MT.*
    FROM MAIN_TBL MT
        JOIN LARGE_TBL LT ON LT.LT_ID = MT.MT_ID
    WHERE LT.IDX_2 = 'G' OR LT.COL_1 <> 'Y' OR LT.COL_1 IS NULL)
SET
    MT.STOP_FLAG = 'SF01',
    MT.ES = 'E',
    MT.PW = 'W'
    MT.UPDATE_DT = SYSDATE
WHERE 
    MT.STOP_FLAG IS NULL
    AND MT.IDX_2 = 'G'
    AND MT.ES IS NULL
    AND MT.SS = 'C'
    AND MT.PW = 'A'

那么基本上跟

UPDATE MAIN_TBL MT
SET MT.STOP_FLAG = 'SF01'
WHERE {whatever condition}

---

您的条件可以有效地重新写入为检查lt.col_1字段的值是否不等于“Y”（即

lt.col_1为null或lt.col_1！=“Y”

）。我已经构建了一个快速测试用例，使用您的旧检查方法和新的：

WITH t1 AS (SELECT 1 mt_id, 10 val FROM dual UNION ALL
            SELECT 2 mt_id, 20 val FROM dual UNION ALL
            SELECT 3 mt_id, 30 val FROM dual UNION ALL
            SELECT 4 mt_id, 40 val FROM dual UNION ALL
            SELECT 5 mt_id, 50 val FROM dual),
     t2 AS (SELECT 2 lt_id, 'F' idx_2, NULL col_1 FROM dual UNION ALL
            SELECT 3 lt_id, 'G' idx_2, NULL col_1 FROM dual UNION ALL
            SELECT 4 lt_id, 'G' idx_2, 'N' col_1 FROM dual UNION ALL
            SELECT 5 lt_id, 'G' idx_2, 'Y' col_1 FROM dual)
SELECT 'new_way' qry,
       t1.mt_id,
       t1.val,
       CASE WHEN t2.col_1 is null or t2.col_1 != 'Y' THEN 'SF01' END new_stop_val
FROM   t1
       LEFT OUTER JOIN t2 ON t1.mt_id = t2.lt_id AND idx_2 = 'G'
UNION ALL
SELECT 'old_way' qry,
       t1.mt_id,
       t1.val,
       CASE WHEN NOT EXISTS (SELECT 1 FROM t2 WHERE t2.LT_ID = t1.MT_ID AND t2.IDX_2 = 'G')
                 OR (SELECT t2.COL_1 FROM t2 WHERE t2.LT_ID = t1.MT_ID AND t2.IDX_2 = 'G') IS NULL
                 OR (SELECT t2.COL_1 FROM t2 WHERE t2.LT_ID = t1.MT_ID AND t2.IDX_2 = 'G') <> 'Y'
                 THEN 'SF01'
       END new_stop_val
FROM   t1
ORDER BY mt_ID, qry;

QRY          MT_ID        VAL NEW_STOP_VAL
------- ---------- ---------- ------------
new_way          1         10 SF01
old_way          1         10 SF01
new_way          2         20 SF01
old_way          2         20 SF01
new_way          3         30 SF01
old_way          3         30 SF01
new_way          4         40 SF01
old_way          4         40 SF01
new_way          5         50 
old_way          5         50 

---

您的条件可以有效地重新写入为检查lt.col_1字段的值是否不等于“Y”（即

lt.col_1为null或lt.col_1！=“Y”

）。我已经构建了一个快速测试用例，使用您的旧检查方法和新的：

WITH t1 AS (SELECT 1 mt_id, 10 val FROM dual UNION ALL
            SELECT 2 mt_id, 20 val FROM dual UNION ALL
            SELECT 3 mt_id, 30 val FROM dual UNION ALL
            SELECT 4 mt_id, 40 val FROM dual UNION ALL
            SELECT 5 mt_id, 50 val FROM dual),
     t2 AS (SELECT 2 lt_id, 'F' idx_2, NULL col_1 FROM dual UNION ALL
            SELECT 3 lt_id, 'G' idx_2, NULL col_1 FROM dual UNION ALL
            SELECT 4 lt_id, 'G' idx_2, 'N' col_1 FROM dual UNION ALL
            SELECT 5 lt_id, 'G' idx_2, 'Y' col_1 FROM dual)
SELECT 'new_way' qry,
       t1.mt_id,
       t1.val,
       CASE WHEN t2.col_1 is null or t2.col_1 != 'Y' THEN 'SF01' END new_stop_val
FROM   t1
       LEFT OUTER JOIN t2 ON t1.mt_id = t2.lt_id AND idx_2 = 'G'
UNION ALL
SELECT 'old_way' qry,
       t1.mt_id,
       t1.val,
       CASE WHEN NOT EXISTS (SELECT 1 FROM t2 WHERE t2.LT_ID = t1.MT_ID AND t2.IDX_2 = 'G')
                 OR (SELECT t2.COL_1 FROM t2 WHERE t2.LT_ID = t1.MT_ID AND t2.IDX_2 = 'G') IS NULL
                 OR (SELECT t2.COL_1 FROM t2 WHERE t2.LT_ID = t1.MT_ID AND t2.IDX_2 = 'G') <> 'Y'
                 THEN 'SF01'
       END new_stop_val
FROM   t1
ORDER BY mt_ID, qry;

QRY          MT_ID        VAL NEW_STOP_VAL
------- ---------- ---------- ------------
new_way          1         10 SF01
old_way          1         10 SF01
new_way          2         20 SF01
old_way          2         20 SF01
new_way          3         30 SF01
old_way          3         30 SF01
new_way          4         40 SF01
old_way          4         40 SF01
new_way          5         50 
old_way          5         50 

---

请通读链接并尝试创建要更新的过程。如果您遇到任何困难，请联系我们。你的

案例

表达式看起来很奇怪。你选择同一个表9次，你怎么能期望良好的性能？尝试只选择一次表大。\u TBL。请通读链接并尝试创建要更新的过程。如果您遇到任何困难，请联系我们。你的

案例

表达式看起来很奇怪。你选择同一个表9次，你怎么能期望良好的性能？请尝试只选择一次表大。\u TBL。您能告诉我这条

ON

子句将要完成什么吗：

（tgt.rowid=src.r\u id）

？我们是否应该将

SELECT

子句改为

USING（选择mt.rowid、mt.mt\u id、mt.idx\u 2

和

ON

子句改为

（tgt.mt\u id=src.mt\u id和tgt.idx\u 2='G'）

？我使用rowid作为联接条件，因为我不知道表的主键。如果愿意，您可以切换到使用主键，只要您不尝试更新任何主键列（此时您必须在rowid上联接）。您能告诉我这条关于的

子句将要完成什么吗：
（tgt.rowid=src.r\u id）
？我们是否应该使用（选择mt.rowid、mt.mt\u id、mt.idx\u 2

和

关于

子句的

（tgt.mt\u id=src.mt\u id和tgt.idx\u 2='G'）将
子句更改为
？我使用rowid作为联接条件，因为我不知道表的主键。如果愿意，您可以切换到使用主键，只要您不尝试更新任何主键列（此时您必须在rowid上联接）。
MERGE INTO main_table tgt
USING (SELECT mt.rowid, r_id,
              CASE WHEN lt.col_1 is null or lt.col_1 != 'Y' THEN 'SF01'
                   WHEN lt.col_2 is null or lt.col_2 != 'Y' THEN 'SF02'
                   ELSE mt.stop_flag -- null
              END new_stop_flag,
              CASE WHEN NVL(lt.col1, 'N') != 'Y' THEN 'E'
                   WHEN NVL(lt.col2, 'N') != 'Y' THEN 'E'
                   ELSE mt.es -- null
              END new_es,
              CASE WHEN NVL(lt.col_1, 'N') != 'Y' THEN 'W'
                   WHEN NVL(lt.col_2, 'N') != 'Y' THEN 'W'
                   ELSE mt.pw
              END new_pw
       FROM   main_table mt
              LEFT JOIN large_table lt ON (mt.mt_id = lt.lt_id AND lt.idx_2 = 'G')
       WHERE  mt.stop_flag IS NULL
       AND    mt.idx_2 = 'G'
       AND    mt.es IS NULL
       AND    mt.ss = 'C'
       AND    mt.pw = 'A') src
  ON (tgt.rowid = src.r_id)
WHEN MATCHED THEN
  UPDATE tgt.stop_flag = src.new_stop_flag,
         tgt.es = src.es,
         tgt.pw = src.pw;