When it comes to designing a database in SQL Server, the initial design plays a crucial role in the success of any software project. A well-designed database ensures efficient data storage, retrieval, and maintenance. One important aspect of database design is the use of lookup tables or reference tables.
A lookup table is a table that contains a list of values that are commonly used in other tables. Instead of storing these values directly in multiple tables, we can reference them from a single lookup table. This approach not only simplifies the database structure but also improves performance and maintainability.
Let’s consider an example to understand the concept of lookup tables. In a database, we have two tables: “Employee” and “Job”. The “Employee” table has a column called “Job_ID” which contains integer values. On the other hand, the “Job” table contains the job descriptions. Instead of storing the job descriptions directly in the “Employee” table, we can reference them from the “Job” table using a foreign key relationship.
Similarly, in another example, we have a “Customer” table with a column called “State” which references the “StateCode” column in the “State” table to retrieve the corresponding state name. This eliminates the need to store the state names directly in the “Customer” table.
In a database with multiple tables, there may be several scenarios where lookup tables are required. Instead of creating separate lookup tables for each scenario, we can create a “GenericLookup” table that can be used in most cases. This table acts as a centralized repository for storing lookup values.
The advantages of using a “GenericLookup” table are:
- We can store integer values in most of the data columns and keep the descriptions in the “GenericLookup” table. This improves performance as numeric columns are generally faster to process than non-numeric columns.
- Maintainability becomes easier. With a “GenericLookup” table, we only need a few stored procedures (Insert/Update/Delete) to manage the data instead of creating separate procedures for each lookup table.
- Centralized information in one place. The “GenericLookup” table serves as a data dictionary, providing a single source of truth for lookup values.
To retrieve information from the “GenericLookup” table, we can create a stored procedure that accepts the category as a parameter. The stored procedure will then fetch the relevant data from the “GenericLookup” table based on the provided category.
Here’s an example of how to retrieve data from the “GenericLookup” table:
DECLARE @strCategory VARCHAR(100)
SET @strCategory = 'Customer.CreditCardType'
SELECT intID, strCode, strDescription
FROM dbo.GenericLookup (NOLOCK)
WHERE strCategory = @strCategory
By using a “GenericLookup” table, we can simplify the database design, improve performance, and enhance maintainability. It provides a flexible and efficient solution for managing lookup values in SQL Server.
Remember, a well-designed database is the foundation of a successful software project. So, make sure to consider the use of lookup tables in your SQL Server database design to achieve optimal performance and maintainability.