SQL Constraint and Keys Archives - Page 6 of 14 - SQL Authority with Pinal Dave

SQL SERVER – Create Unique Constraint on Table Column on Existing Table

January 11, 2014

Here is the question I received on twitter. “Can we create a unique constraint on table column on Existing Table?” Of course Yes! Here is how you can create a unique constraint on the table which already exist in our system. USE tempdb GO -- Create Table CREATE TABLE Table1…

SQL SERVER – Disable All the Foreign Key Constraint in Database – Enable All the Foreign Key Constraint in Database

April 29, 2013

Pinal Dave

SQL, SQL Server, SQL Tips and Tricks

SQL Constraint and Keys

Here is an email I received during the weekend. “Hi Pinal, I am a senior tester in the leading organization and we have two different environments 1) Testing 2) Production. As a part of the testing we want to insert garbage data into the database system and see how the application…

SQL SERVER – Fix: Error: 1505 The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name and the index name

February 5, 2013

Pinal Dave

SQL, SQL Server, SQL Tips and Tricks

SQL Constraint and Keys, SQL Error Messages

Here is another example where the error messages are very clear but often developers get confused with the message. I think the reason for the confusion is the word “Key” used in the error message. After I explained this to a developer who sent me the error he realize that…

SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – Part 1 of 2

August 16, 2012

Pinal Dave

SQL

SQL Constraint and Keys, SQL Server

Social media has created an Always Connected World for us. On the second day of the event after the learning was over, I noticed lots of notification from my friend on my various social media handle. He had connected with me on Twitter, Facebook, Google+, LinkedIn, YouTube as well SMS, WhatsApp on the phone, Skype messages and not to forget with a few emails. I right away called him up. Let us learn about ON UPDATE CASCADE and ON DELETE CASCADE.

SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 6 of 31

July 6, 2011

Pinal Dave

SQL Interview Questions and Answers

SQL Constraint and Keys, SQL Index, SQL Server

Please read the Introductory Post before continuing reading interview questions and answers.

SQL SERVER – How to ALTER CONSTRAINT

April 24, 2011

Pinal Dave

SQL, SQL Server, SQL Tips and Tricks

SQL Constraint and Keys, SQL Scripts

After reading my earlier blog post SQL SERVER – Prevent Constraint to Allow NULL. I recently received question from user regarding how to alter the constraint. No. We cannot alter the constraint, only thing we can do is drop and recreate it. Here is the CREATE and DROP script. CREATE…

SQL SERVER – Prevent Constraint to Allow NULL

April 21, 2011

Pinal Dave

SQL, SQL Server, SQL Tips and Tricks

SQL Constraint and Keys, SQL Scripts

With naked eyes, we often spot the evident problems but the specific details are missed many a time. Something similar happened recently. One of the blog readers sent me an email asking about a bug in how CHECK CONSTRAINT works. He suggested that check constraint accepts NULL even though the…