Foreign Keys (FK)

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SQL Server Foreign Key Update and Delete Rules

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Foreign key constraints are an integral part of SQL Server database design. These are used to maintain integrity among related data in different tables. While implementing update and delete operations on values in the parent table (referenced table with primary key) we have to consider the impact on related values in the child table. SQL Server provides different rules for managing the effect of updates and deletes on child table values. How can these rules be used effectively without threatening the relational integrity?

2011-05-03

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Question of the Day

The Read Committed Snapshot Isolation behaviour

I am currently working with Sql Server 2022 and AdventureWorks database. First of all, let's set the "Read Committed Snapshot" to ON: 

use master;
go

alter database AdventureWorks set read_committed_snapshot on with no_wait;
go
Then, from Session 1, I execute the following code: 
--Session 1
use AdventureWorks;
go

create table ##t1 (id int, f1 varchar(10));
go

insert into ##t1 values (1, 'A');
From another session, called Session 2, I open a transaction and execute the following update: 
--Session 2
use AdventureWorks;
go

begin tran;
update ##t1 
set f1 = 'B'
where id = 1;
Now, going back to Session 1, what happens if I execute this statement? 
--Session 1
select f1
from ##t1
where id = 1;
 

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