SQL with (NoLock), with (ReadPast)

---------------Create Tabletmp1 (IDint Primary Key, namenvarchar( -))-----------Insert  intoTMP1 (Id,name)Values(1,'Zhsan1');Insert  intoTMP1 (Id,name)Values(2,'LISI1');-------------------------------Select *  fromTmp1

UPDATE statement locks the database

-- --------------------------- begin Tran tran1     Update Set name='zhsan'where id=1 -- ----------------------------- Select *  from TMP1

The query has been in progress, and the table is locked.

-- ----------------------------- Update Set name='Lisi'where id=2-- ----------------------------- Select *  from where Id>1

-- ----------------------------- Delete  from where id=2-------------------------------Select*  fromwhere ID>1

Query, update, delete the row of data except the lock can be successful, indicating that only the id=1 of the locked row, the other rows of the query, update and delete no impact

Insert statement

-- ----------------------------- Insert  into Values (3,'Lisi') -- ----------------------------- Select *  from where ID>1

Successful execution of the results, indicating that the insert is not affected

First restore the database to

-- --------------------------- begin Tran tran1     Update Set name='zhsan'where id=1

With (Readpast) and with (NOLOCK)

-- ----------------------------- Select *  from  with (Readpast)

-- ----------------------------- Select *  from  with (NOLOCK)

With (Readpast) ignores the locked line, with (NOLOCK) does not

SQL with (NoLock), with (ReadPast)