The optional lock-request-clause specifies
the type of lock that the database manager is to acquire and hold.
SHARE
Concurrent processes can acquire SHARE or UPDATE locks on the
data.
UPDATE
Concurrent processes can acquire SHARE locks on the data, but
no concurrent process can acquire an UPDATE or EXCLUSIVE lock.
EXCLUSIVE
Concurrent processes cannot acquire a lock on the data.
The lock-request-clause applies
to all base table and index scans required by the query, including
those within subqueries, SQL functions and SQL methods. It has no
affect on locks placed by procedures, external functions, or external
methods. Any SQL function or SQL method called (directly or indirectly)
by the statement must be created with INHERIT ISOLATION LEVEL WITH
LOCK REQUEST (SQLSTATE 42601). The lock-request-clause cannot
be used with a modifying query that might activate triggers or that
requires referential integrity checks (SQLSTATE 42601).
