How to handle multiple user updating record same time in DB

Thanks for the reply @Madan Sorab it realy what i wanted

 

actually now I have two dobuts 

 

1. if site is using by millios of user, if suppos hundreds of user is trying to update the same record in this schenario, wht will happen, plz explain how it will work.

 

2. as u given example:  Two people pull up the record for employee 'Bob Jones'. Both see the same data for Bob because no changes have been made. The first person makes some changes and submits them.

now the other person has old data, he does not have data updated by first person. now this person make his changes and submit the data then it could be wrong, bcz this person is updatin the old record, suppose there are 10 filed on the form person a updated from 1-5, 

now person b updatin from 6-10 and submit, but it will update 1-5 also with the values which person b loader befor.

 can you please explain how can we handle this type of schenario.

 

thanks

There is one point that should be brought up. Locks are only put into place when a DML operation is started (i.e. an UPDATE statement is executed). The locks are only held until a transaction-ending operation is performed (i.e. a COMMIT, ROLLBACK, or DDL operation). This is important because in human terms, it is possible for two people to be 'updating the same row at the same time', when in fact it is not the case for the database.

 

Take for example a database updated by a web interface. Two people pull up the record for employee 'Bob Jones'. Both see the same data for Bob because no changes have been made. The first person makes some changes and submits them. The row is locked, changed, and unlocked. The second person will not see these changes on their screen. The second person makes some changes and submit them. The row is locked, changed and unlocked.

 

Because the UPDATE and COMMIT operations happen (almost assuredly) in a fraction of a second, the updates performed by the two users may well happen less than a second from each other. In human terms, they were updating the same row at the same time. From the standpoint of the database, they were not.