Know What is Lookup Table in SQL Server
SQL Server is the widely being used relational database management system as it allows to store large amount of data in the relational tables. Users can create any number of tables with different fields to store the data in a consistent manner. The organizations which handles thousands of records in a database can easily make the use of a special kind of table known as SQL Server lookup tables to maintain the data integrity among large number of records.
It can be basically considered as a reference to link the related tables with the help of a unique primary key. The lookup tables in SQL Server can also be called as reference table as the data in lookup table is referenced from other related tables.
Brief History of SQL Lookup Table – The Journey
From the early days of relational databases use in the 1970s, lookup tables are used in SQL databases. It acts as a centralized reference point for commonly used data files with the aim of accessing & updating them on multiple databases easily.
The table contains a list of values like names, codes, & identifiers that are used by database admins. The sole purpose of these values is to build relationships among tables or to add context to the data stored in these respective tables.
Now, with time passing, SQL tables have become a standard feature of SQL databases. In addition, it is now in use by a wide range of applications as well. Users can find lookup tables in software, web & mobile apps nowadays. As we know that cloud computing is the thing of today, the lookup tables are now a significant tool for managing & accessing data files in a more effective & efficient manner.
Learn About SQL Server Lookup Tables
Consider a situation, where an organization needs to maintain a database to store its employee information. A SQL table is created with the fields (Emp ID, Name, Membership). Only four membership options are present in the organization, so the membership field can hold a value out of the four different options. In case of thousand records, the membership field will be repeating among all the records and this field is a kind of static field, which does not change frequently.
So, the user can choose to create a child table i.e., lookup table containing Emp id and membership fields of the main table. So, we can easily reference the fields of the child table with the main table of the database.
Syntax of Table
The following SQL query attempts to create a lookup table in SQL for the main table Employee:
CREATE TABLE Employee (EmpId int NOT NULL, name character varying NOT NULL, membership character varying NOT NULL );
CREATE TABLE links_type_lookup (EmpId int NOT NULL, membership character varying NOT NULL);
ALTER TABLE ONLY links_type_lookup ADD CONSTRAINT links_type_lookup_pkey PRIMARY KEY (EmpId);
Some of the features possessed by the lookup tables are:
- They contain the descriptive data related to the main table.
- They are relatively smaller than the main table.
- They are generally insert-and-read tables as they are updated rarely.
- They generally store data in the form of key-value pair.
How to Create a Lookup Table in SQL Server Database?
Step-1. Determine Purpose
Understand the use of your lookup table & what are the values that you need to store in it. For instance, a user creating a product category table must have fields like Category ID, Category Name & a description about the category.
Step-2. Create Table
The second step here is to create a new table using the CREATE TABLE statement below-mentioned syntax as follows:
CREATE TABLE product_categories ( category_id INT PRIMARY KEY, category_name VARCHAR(50) NOT NULL, category_description VARCHAR(255) );
This query creates a table “Product Categories” with three columns as “category_id”, “category_name”, and “category_description” respectively.
Step-3. Insert Data
With the “Insert Into” statement, users can add the data in the table like:
INSERT INTO product_categories (category_id, category_name, category_description) VALUES (1, 'Electronics', 'Electronic devices and accessories’);
Repeating this third step for each value is how users can easily add more values. After creating the table, simply reference it with other tables or apps.
Importance of Using Lookup Tables
Lookup tables play a considerable role in maintaining the data integrity of the entire database. Users are advised to make use of lookup tables to easily manage large database. Some of the advantages of using lookup table in SQL are:
1. Storage Management
Since, lookup tables store the frequently repeating data as a reference to the main table. So, it prevents the repetition of same data in the main table and helps to save the memory.
2. Better Performance
When a query is made, the data can be easily referenced from the lookup table. So, it improves the performance of the system by utilizing less I/O resources, memory & CPU utilization.
3. Easy Data Modification
If any changes are to be made to a field, then they can be easily made at once on the lookup table. It will automatically update the referenced fields of the main table. So, in this way lookup tables help to easily modify the data by maintaining data integrity.
4. Faster Search
As the lookup table in SQL server has small size due to limited columns, so it becomes easy for user to search within the limited data from the lookup table and save time.
5. Easier Data Updates
When a user need to update the table values that are commonly used, they can do that by updating the values in lookup tables easily. The change made here will automatically reflect in all other tables respectively.
As we know that lookup tables are used in a variety of applications. Moreover, it can store any type of value like simple IDs as well as complex data structures. Thus, it comes out as a versatile tool for managing & accessing multiple applications.
The above article has been aimed to make the users learn the concept of lookup table in SQL Server. Users are suggested to make the use of lookup tables for easy handling a large database. Evidently, the number of lookup tables created may depend on the size and complexity of the database as SQL Server does not impose any limitation on the number of lookup tables.