Question - Must Locks Be Explicitly Requested Or Is Implicit Locking Possible?
Answer -
Locks can be requested implicitly by the database system or explicitly by you (using the relevant SQL statements).
a) Requesting locks implicitly:
All modifying SQL statements (for example, INSERT, UPDATE, DELETE) always request an exclusive lock.
You can select the lock operation mode by specifying an isolation level when you open the database session.
Depending on the specified isolation level, locks are then implicitly requested by the database system when the SQL statements are processed.
b) Requesting locks explicitly:
You can assign locks explicitly to a transaction using the LOCK statement, and you can lock individual table lines by specifying a LOCK option in an SQL statement. This procedure is possible at each isolation level. In addition, you can use the LOCK option to temporarily change the isolation level of an SQL statement.