問題更新查詢

Question

我有一個查詢

UPDATE Table_1 SET Col1='Y' WHERE ROWID IN (
    select ROWID from (
     SELECT BUS_ID, 
       row_number() over (partition by BUS_ID order by BUS_ID) dupe_count, 
       rowid 
     from Table_1 
     WHERE col2 <> 1 
      AND col3 <> 1 
     order by dbms_random.value 
    ) ft 
    where ft.dupe_count = 1 
     AND ROWNUM <= 1000 
); 

只更新1000臺TABLE_1行。

但如果我寫

UPDATE Table_1 SET Col1='Y' WHERE ROWID IN (
    select ROWID from (
     SELECT BUS_ID, 
       row_number() over (partition by BUS_ID order by BUS_ID) dupe_count, 
       rowid 
     from Table_1 
     WHERE col2 <> 1 
      AND col3 <> 1 
     order by dbms_random.value 
    ) ft 
    where ft.dupe_count = 1 
     and Table_1.BUS_ID = ft.BUS_ID 
     AND ROWNUM <= 1000 
); 

它更新表中的所有行，不論RoWNUM <= 1000即如果我添加

Table_1.BUS_ID = ft.BUS_ID 

則更新滿足col2<> 1 AND col3<> 1 and ft.dupe_count=1所有行。 該表具有以下結構：

BUS_ID | col1 | col2 | col3 
    1 |  | 0 | 0 
    2 |  | 0 | 0 
    1 |  | 0 | 0 
    3 |  | 1 | 1. 

任何想法，爲什麼它happening.Please幫助。

Answer 1

Niraj，

對每個表格評估一個普通的子查詢。針對每一行評估相關子查詢。並且您已在第二條更新聲明中將子查詢與行Table_1.BUS_ID = ft.BUS_ID相關聯。如果它對每一行進行評估，那麼它總是會滿足謂詞。

Regards，
Rob。