Shulou(Shulou.com)06/01 Report--

Lock data rows

Select * from emp t where t. DeptNozzles 20'

For update nowait

This locks the row of data in the emp table with deptno = 20

Note: after locking through for update, these rows cannot be modified, but they can still be queried.

For update and for update nowait

Use for update to lock the row, and execute update,delete,select on the line.. For update statements are blocked, that is, execution continues after waiting for the lock to be released

Use for update nowait to lock the row, and execute update,delete,select on the line.. For udapte statement, will immediately return a "ORA-00054:resource busy" error, do not have to wait for the release of the lock to continue to hold

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