You may have seen the term “RID lookup” when reading about heap tables, or perhaps when viewing the query plan for a query against a heap in SQL Server.
But what exactly is a RID lookup? And what exactly is a RID?
Let’s find out.
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Compound Keys Explained
In SQL databases, a compound key is a type of primary key that consists of two or more columns combined to uniquely identify each row in a table. The key columns are used together as a single unit to ensure uniqueness.
Some within the SQL community define compound keys as composite primary keys comprising of foreign keys from other tables, so there doesn’t seem to be an agreed consensus on the precise definition.
With that in mind, let’s explore these definitions of compound keys.
Continue readingWhat is a Composite Key in SQL?
In SQL, a composite key is a key that consists of two or more columns used together to uniquely identify a record in a table. The combination of these columns creates a unique identifier, even though the individual columns might not be unique by themselves.
Continue readingUnderstanding the RID Lookup in SQL Server: How It Affects Performance
If you’ve spent any time working with heaps in SQL Server, you may have seen the RID lookup in the query plan. And if you haven’t, chances are it’s because you either didn’t look at the query plan, or the queries used full table scans.
In any case, it pays to understand what a RID lookup is and how it affects query performance. If we ever see RID lookup in the query plan, it could be a good opportunity to see if we can make changes that will improve performance.
Continue readingWhat is a Surrogate Key in SQL?
In SQL and relational database design in general, an important concept is the identification of unique rows in a table. A surrogate key is one method for achieving this.
Understanding what surrogate keys are, and how they differ from natural keys, is crucial for database administrators, developers, and anyone involved in data modeling or management.
In this article we’ll explore what the surrogate key is, how it differs from the natural key, and examples of implementing it in SQL.
Continue readingUnderstanding the Covering Index in SQL
In SQL, adding an index to a table can provide us with a significant performance boost, especially if it’s a covering index for commonly run queries.
But what exactly is a covering index?
Let’s find out.
Continue readingWhat is a Superkey Key in SQL?
There are various key types in SQL, each with their own characteristics. Some of these can be enforced with a constraint of one kind or another. Others are not necessarily enforced with a constraint, but are more of an abstract notion, albeit, an important one. These key types consist of one or more columns with certain characteristics that qualify it as the particular key.
One such key type is the superkey.
Continue readingUnderstanding Self-Referencing Foreign Keys: A Beginner’s Tutorial
In relational databases, a foreign key is typically a field that is linked to another table‘s primary key field in a relationship between two tables.
However, there’s also a type of foreign key we call the self-referencing foreign key. The self-referencing foreign key refers to a field within the same table, creating a relationship between rows in the same table.
Continue readingWhat is a Trigger in SQL?
In SQL databases, triggers can play a significant role in automating responses to specific events within a database. Whether we’re dealing with data validation, logging changes, or enforcing business rules, SQL triggers can be a handy tool to ensure that certain actions are taken automatically when certain conditions are met.
This article covers what SQL triggers are, how they work, and provides an example to illustrate their use.
Continue readingWhat is a Natural Key in SQL?
In relational database design, the concept of a “key” is fundamental. Keys are essential for uniquely identifying records in a table, ensuring data integrity, and facilitating efficient data retrieval. Among the different types of keys used in SQL, the natural key is one that often sparks discussion among database designers, especially when compared with the surrogate key.
Let’s explore the concept of a natural key, its advantages and disadvantages, and look at a practical example to illustrate its use.
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