sql query with nolock

Label:There are many articles about nolock in the blog Park, most of which are well written, for example: http://www.cnblogs.com/huangxincheng/p/4292320.html This is a personal note that only combines individual items. Nolock methods of use such as: SELECT * FROM table1 with (NOLOCK) With the "lock hint" behind, there are many kinds of locking hints, such as tabl

When with and as, the expression defines a SQL sentenceCases:WithSonword as(SELECT * FROM person)SELECT * FROM Studentwhere name in (select name from Sonword)EquivalentSELECT * FROM Studentwhere name in (select name from person)With (NOLOCK)Typically used in SELECT statements, data that is locked by a transaction can be readImproves SQL

SQL Server NOLOCK, HOLDLOCK, UPDLOCK, TABLOCK, Tablockxposted 3 years ago ⁄sql Server ⁄ no comments ⁄ reading 3,483 NOLOCK (without lock) When this option is selected, SQL Server does not add any locks when reading or modifying data. In this case, it is possible for th

What exactly does NOLOCK in SQL Server mean?Typically used in such statements: SELECT * from T with (NOLOCK)Nolock is a non-locking query. Ability to read data locked by transactions, also known as dirty reads.Description:causes the current session's

There was one thing I remember, that year just came Ctrip soon, was arranged to write an interface, for the Penguin company to call their employees travel information, and then I rinsed to write good, on-line, after about one months ... The DBA has reported a large number of lock timeouts in the database, and promptly sent the email to our department based on the source of SQL, indicating that the SQL read

---------------Create Tabletmp1 (IDint Primary Key, namenvarchar( -))-----------Insert intoTMP1 (Id,name)Values(1,'Zhsan1');Insert intoTMP1 (Id,name)Values(2,'LISI1');-------------------------------Select * fromTmp1UPDATE statement locks the database-- --------------------------- begin Tran tran1 Update Set name='zhsan'where id=1 -- ----------------------------- Select * from TMP1The query has been in progress, and the table is locked.-- -----

1, NOLOCK (without lock)When this option is selected, SQL Server does not add any locks when reading or modifying data. In this case, it is possible for the user to read the data in the incomplete transaction (uncommited Transaction) or rollback (roll back), known as "dirty data."2. HOLDLOCK (Hold Lock)When this option is selected, SQL Server will persist this sh

the obtained scroll lock depends on the cursor concurrency option and the lock prompt in the Select statement of the cursor. Lock prompt read-only optimistic value optimistic row version control lock No prompt not locked update NOLOCK not locked HOLDLOCK sharing update UPDLOCK error Update TABLOCKX Error unlocked unlocked update other unlocked update * The specified NOLOCK prompt will make the table specif

the data is consistent, but nothing is perfect. The cost of the Begin Tran is that all the resources locked by the SQL statements cannot be released until the commit is committed before committing.It can be seen that if the BEGIN TRAN too many SQL statements, the performance of the database is poor. Before this large transaction commits, it is bound to block other statements, resulting in many blocks.The p

Http://www.cnblogs.com/dubing/archive/2011/12/09/2278090.htmlRecently the company has come to a very tiger DBA 10几 years of experience here is called Cai Teacher. Let us share the precious wealth that Cai Lao has brought to us, with the consent of our Chua. Welcome other DBAs to shoot bricks Directory1. What is the execution plan? The execution plan is dependent on what information.2, unified SQL statement to reduce parsing overhead3. Reduce the

Directory1. What is the execution plan? The execution plan is dependent on what information.2, unified SQL statement to reduce parsing overhead3. Reduce the nesting of SQL statements4. Staging intermediate results using temporary table5. The OLTP system SQL statement must take a binding variable6. The spy problem of the bound variable of the tilted field7. Begin