我试着把它放在句子里，但给一个例子会更好：
SELECT * FROM someTable WHERE id = someID;
returns no rows
...
some time passes (no inserts are done to the table and no ID updates)
...
SELECT * FROM someTable WHERE id = someID;
returns one row!
有可能某些DB机制阻止第一个SELECT返回行吗？
Oracle log has no errors.
No transactions are rolled back when two selects are executed.
You can t see uncommitted data in another session. When did the commit happen?
EDIT1: Are you the only one using this database? Or did/do you have multiple sessions?
I think in another session you or someone else has inserted this row, you do your select and you don t see this row. After that a commit happens in the other session (maybe implicit because a session is closed) and then you see this row when you select again.
I can think of other explanations, but I first want to know are you only one using this database.
使用Oracle提供的读一致性，您不应该看到出现这样的行。如果您在某种自动提交的模式下运行，使得每个语句都是一个独立的事务，则不违反读一致性。您使用哪个程序访问数据库？我同意其他人的观察;如果您的会话没有插入它，同时没有其他会话处于活动状态，则该行不应出现。我不知道有哪个DBMS会通过自发数据生成来满足自己。
Don t you have scheduled jobs in that Oracle?