SQL Server Locks Question:

SQL Server has 3 main lock types:

Shared: Locks are compatible with other shared and update locks.
Update: Locks are compatible with shared locks.
Exclusive: Locks are not compatible with any other locks.

Apart from lock types, there are transaction isolation levels for managing security among transactions:

READ UNCOMMITTED
READ COMMITTED
REPEATABLE READ
SERIALIZABLE

SQL Server has some locking optimizer hints along with lock types:

NOLOCK
HOLDLOCK
UPDLOCK
TABLOCK
PAGLOCK
TABLOCKX
READCOMMITTED
READUNCOMMITTED
REPEATABLEREAD
SERIALIZABLE
READPAST
ROWLOCK