Manually lock one or more tables.
LOCK TABLE [schema.] table [options] IN lockmode MODE [NOWAIT] LOCK TABLE [schema.] view [options] IN lockmode MODE [NOWAIT] Options: PARTITION (partition) SUBPARTITION (subpartition) @dblink lockmodes: EXCLUSIVE SHARE ROW EXCLUSIVE SHARE ROW EXCLUSIVE ROW SHARE* | SHARE UPDATE*
If NOWAIT is omitted Oracle will wait until the table is available.
Several tables can be locked with a single command - separate with commas
e.g.LOCK TABLE table1,table2,table3 IN ROW EXCLUSIVE MODE;
Default Locking Behaviour
A pure SELECT will not lock any rows.
INSERT, UPDATE or DELETE's - will place a ROW EXCLUSIVE lock.
SELECT…FROM…FOR UPDATE NOWAIT - will place a ROW EXCLUSIVE lock.
Multiple Locks on the same rows with LOCK TABLE
Even when a row is locked you can always perform a SELECT (because SELECT does not lock any rows) in addition to this, each type of lock will allow additional locks to be granted as follows.
ROW SHARE = Allow ROW EXCLUSIVE or ROW SHARE or SHARE locks to be granted to the locked rows.
ROW EXCLUSIVE = Allow ROW EXCLUSIVE or ROW SHARE locks to be granted to the locked rows.
SHARE ROW EXCLUSIVE = Allow ROW SHARE locks to be granted to the locked rows.
SHARE = Allow ROW SHARE or SHARE locks to be granted to the locked rows.
EXCLUSIVE = Allow SELECT queries only
Although it is valid to place more than one lock on a row, UPDATES and DELETE's can still cause a wait if a conflicting row lock is held by another transaction.
* = Oracle 6 optionincluded for compatibility
Related Oracle Commands:
DBA_ALL_TABLES ALL_ALL_TABLES USER_ALL_TABLES
DBA_TABLES ALL_TABLES USER_TABLES TAB