SQL SERVER – Locking Hints and Examples

Locking Hints and Examples are as follows. The usage of them is the same but the effect is different.

ROWLOCK
Use row-level locks when reading or modifying data.

PAGLOCK
Use page-level locks when reading or modifying data.

TABLOCK
Use a table lock when reading or modifying data.

DBLOCK
Use a database lock when reading or modifying data.

UPDLOCK
UPDLOCK reads data without blocking other readers, and updates it later with the assurance that the data has not changed since the last read.

XLOCK
Use exclusive locks instead of shared locks while reading a table, and use hold locks until the end of the statement or transaction.

HOLDLOCK
Use a hold lock to hold a lock until completion of the transaction, instead of releasing the lock as soon as the required table, row, or data page is no longer required.

NOLOCK
This does not lock any object. This is the default for SELECT operations. It does not apply to INSERT, UPDATE, and DELETE statements.

Examples:

SELECT OrderID
FROM Orders WITH (ROWLOCK)
WHERE OrderID BETWEEN 100
AND 2000

UPDATE Products WITH (NOLOCK)
SET ProductCat = 'Machine'
WHERE ProductSubCat = 'Mac'

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Reference: Pinal Dave (http://blog.SQLAuthority.com)