Tag: primary key

Why Does Oracle Sometimes Not Drop an Index Associated with a Primary Key or Unique Constraint?

Database schema migration is never an easy job. In fact, it can really be a headache, even when you’re working with a familiar system. For example, at times Oracle 10g may not drop the associated index for a primary key or unique constraint that has been dropped. In this article, I am going to explain when and why this happens.The Story:I’ve been working on the development of an e-commerce platform. Before every new platform version release, a migration script is prepared to move the database scheme and data from the old version to the new one. This is done by the database architect in his local environment. Then the migration script is tried out against a test environment that restores the production database and simulates real conditions. (Restoring the production database in the test environment is done using the Oracle 11g Data Pump tool.)

Tip #8 – Setting Your Own Names for Primary Key

Sometimes the naming convention you use requires a specific pattern for the primary keys’ names. That’s why you may want to set your own names for each primary key in your database model instead of using default ones. Go on reading to get to know how to do this in Vertabelo .To give your own name to a primary key, select the table that contains the primary key you want to name:

Tip #6 – How to Create a Multicolumn Primary Key

Primary keys may contain more than one column. Multicolumn primary keys are frequently used for junction tables, which are used to model many-to-many relationships.Select a table: In theTable propertiespanel on the right, check all the columns that you want inside the key: Now, you have a multicolumn primary key created: You can check out your SQL code by clicking theSQL previewbutton in the top right corner:

SQL Server Datatypes: Common Modeling Dilemmas

When designing a database, early decisions can have a huge impact on the performance and storage requirements. These decisions can be difficult to change later, as most subsequent work will depend on the physical model. This article highlights some common design decisions, flaws, and misconceptions.Creating a Primary Key: Uniqueidentifer or IntegerWhen defining a surrogate primary key for a table, two options are the most common: Integer and UniqueIdentifier (aka.Globally Unique Identifiers

On Keys

Today we continue our series of posts on data normalization. In the previous post on data normalization I explained what functional dependency is. Today we will talk aboutcandidate keysin a table.A candidate key is a set of columns such thatall other columns in the table are dependent on it, and the set isminimal, that is if you remove a column, then the resulting set is not a candidate key.Example: Table Person