Prevents other concurrent transactions from accessing or modifying a table.
LOCK TABLE table-name [ WITH HOLD ] IN { SHARE | EXCLUSIVE } MODE
Prevents other transactions from modifying the customer table for the duration of the current transaction:
LOCK TABLE customer IN SHARE MODE
table-name The table must be a base table, not a view. As temporary table data is local to the current connection, locking global or local temporary tables has no effect.
WITH HOLD If this clause is specified, the lock is held until the end of the connection. If the clause is not specified, the lock is released when the current transaction is committed or rolled back.
SHARE Prevents other transactions from modifying the table, but allows them read access. In this mode, you can change data in the table as long as no other transaction has locked the row being modified, either indirectly, or explicitly by using LOCK TABLE.
EXCLUSIVE Prevents other transactions from accessing the table. In this mode, no other transaction can execute queries, updates of any kind, or any other action against the table. If a table t is locked exclusively with LOCK TABLE t IN EXCLUSIVE MODE, the default server behavior is to not acquire row locks for t. This behavior can be disabled by setting the SUBSUME_ROW_LOCKS option OFF.
The LOCK TABLE statement allows direct control over concurrency at a table level, independent of the current isolation level.
Whereas the isolation level of a transaction generally governs the kinds of locks that are set when the current transaction executes a request, the LOCK TABLE statement allows more explicit control locking of the rows in a table.
The locks placed by LOCK TABLE in SHARE mode are phantom and anti-phantom locks, which are displayed by the sa_locks procedure as PT and AT.
Sybase Supported in Adaptive Server Enterprise. The WITH HOLD clause is not supported in Adaptive Server Enterprise. Adaptive Server Enterprise provides a WAIT clause that is not supported in Adaptive Server Anywhere.
To lock a table in SHARE mode, SELECT privileges are required.
To lock a table in EXCLUSIVE mode; you must be the table owner or have DBA authority.
