如何防止自连接数据不一致？
How to keep self-joing from data inconsistence?
在RepeatableRead中，即使记录被多次查询，我们也可以保证从同一条记录中检索到相同的值。但是，在定义视图时不允许设置隔离级别。目前，我正在尝试创建一个视图和 SQL 语句，如下所示 SELECT * FROM TBL t1 INNER JOIN TBL t2 ON t1.SEQ = t2.SEQ + 1.
如您所见，我在一个会话中查询了 table 两次。这个查询可以很快，但我不能保证这两个查询之间 table 没有任何变化。这种自连接如何保持数据的一致性？
Oracle 会自动执行此操作。
Statement-Level Read Consistency
Oracle Database always enforces statement-level read consistency, which guarantees that data returned by a single query is committed and consistent for a single point in time.
The point in time to which a single SQL statement is consistent depends on the transaction isolation level and the nature of the query:
- In the read committed isolation level, this point is the time at which the statement was opened. For example, if a
SELECT statement opens at SCN 1000, then this statement is consistent to SCN 1000.
- In a serializable or read-only transaction, this point is the time the transaction began. For example, if a transaction begins at SCN 1000, and if multiple
SELECT statements occur in this transaction, then each statement is consistent to SCN 1000.
- In a Flashback Query operation (
SELECT ... AS OF), the SELECT statement explicitly specifies the point in time. For example, you can query a table as it appeared last Thursday at 2 p.m.
在RepeatableRead中，即使记录被多次查询，我们也可以保证从同一条记录中检索到相同的值。但是，在定义视图时不允许设置隔离级别。目前，我正在尝试创建一个视图和 SQL 语句，如下所示 SELECT * FROM TBL t1 INNER JOIN TBL t2 ON t1.SEQ = t2.SEQ + 1.
如您所见，我在一个会话中查询了 table 两次。这个查询可以很快，但我不能保证这两个查询之间 table 没有任何变化。这种自连接如何保持数据的一致性？
Oracle 会自动执行此操作。
Statement-Level Read Consistency
Oracle Database always enforces statement-level read consistency, which guarantees that data returned by a single query is committed and consistent for a single point in time.
The point in time to which a single SQL statement is consistent depends on the transaction isolation level and the nature of the query:
- In the read committed isolation level, this point is the time at which the statement was opened. For example, if a
SELECTstatement opens at SCN 1000, then this statement is consistent to SCN 1000.- In a serializable or read-only transaction, this point is the time the transaction began. For example, if a transaction begins at SCN 1000, and if multiple
SELECTstatements occur in this transaction, then each statement is consistent to SCN 1000.- In a Flashback Query operation (
SELECT ... AS OF), theSELECTstatement explicitly specifies the point in time. For example, you can query a table as it appeared last Thursday at 2 p.m.