Types of Indexes (Unique, Composite, Full-text)
In SQL database management systems, indexes are an important feature for managing, controlling, or automatically optimizing database query performance, especially when database users are performing heavy, large-volume data read operations. Several types of table query indexes can be created in a database table as needed. Here are some advantages and features of indexes in SQL database tables.
Let’s explore indexing and its types in SQL database management systems in more detail.
Unique Index in Database Management.
A unique index in an SQL database table ensures that all table row values in the indexed table column field are unique. This helps maintain the integrity of the database data by preventing database users from inserting duplicate data values into the table column. When a unique constraint is applied to a table column, such as being defined as a PRIMARY KEY or UNIQUE, a unique index is automatically created to enforce this constraint on the table column field.
Use Case of Unique Index.
- Enforcing uniqueness – This ensures that no duplicate values are inserted or exist in a table column or combination of column fields in any database table defined by the database user, such as Employee ID, Social Security Number, Email, or Employee Name, etc.
Example of a Unique Index.
Consider an employee table where each employee in the database table must have a unique email address.
CREATE UNIQUE INDEX indx_email
ON employee (e-mail);
This CREATE INDEX statement ensures that no two table rows in the employee table have the same email value.
Primary Key – In database tables, SQL databases create a unique index for the primary key column, ensuring that the primary key constraint values are maintained in the table column.
Composite Index (Multi-Column Index) in Database Management.
A composite index (also known as a multi-column index) in an SQL database table is a type of indexing method that is created on more than one table column field in a database table. A composite index is useful when database table queries involve multiple columns in clauses or expressions such as WHERE, JOIN, ORDER BY, or GROUP BY.
Use Cases of Composite Indexes.
- Optimizing Multi-Column Queries – When user-generated queries in a database table are mostly filtered, sorted, or grouped based on multiple table column fields, a composite table index analyzes all those table columns, improving and speeding up query performance.
Example of Composite Indexes.
Let’s consider a sales table with the column fields store_id, product_id, and sale_date. Here, database users mostly query the table to filter data based on both the store_id and product_id table column fields.
CREATE INDEX indx_store_product
ON sales (store_id, product_id);
Here, the composite index improves and speeds up the performance of the sales table for queries like this:
SELECT * FROM sales
WHERE store_id = 789 AND product_id = 901;
The order of the table column fields in a composite index is essential. A composite index is most effective when the database table query filters or sorts the columns in the same order as they appear in the index. For example, a composite index created on store_id and product_id in the sales table is more effective for table queries that filter records first by store_id and then by product_id. However, if database users mostly filter the table columns first by product_id, then the index would be less effective. Therefore, creating a separate index on `product_id` in the sales table might be useful.
Full-Text Index in Database Management.
A full-text index in a database table is a special type of table query index, specifically developed to manage and control full-text search queries in text-based column fields such as TEXT, VARCHAR, etc. A full-text index helps in quickly and efficiently searching for words or sentences within large text fields.
Full-text indexes are used in certain databases that directly support full-text search features and functionality in their database indexing, such as database management software like MySQL, PostgreSQL, or SQL Server. Full-text indexes follow more advanced search mechanisms, such as partial matching, stemming, and ranking in search results.
Use case of a full-text index.
- Text search – When a database user needs to manually find specific words, sentences, or unique patterns within large text data, such as in website blogs, product descriptions, customer reviews, or other types of documentation in a table query.
Example of a full-text index.
Database users can use this to create a full-text index on the description column of the products table in the MySQL database software.
CREATE FULLTEXT INDEX indx_description
ON product (description);
Once a full-text index is created in the database table, database users can use it to perform full-text searches, applying the MATCH() and AGAINST() functions.
SELECT * FROM product
WHERE MATCH(description) AGAINST (‘+desktop +offer ‘ IN BOOLEAN MODE);
This user-created table query will find products in the product table whose descriptions contain the text or words “desktop” and “offer”.
Boolean Search – Full-text indexes in database tables directly support Boolean search features or syntax, allowing database users to perform more advanced table query searches. This includes adding or removing words in the search query (+, -), finding sentences or phrases in the query, or using special wildcards (*), etc.
Conclusion on Types of Indexes (Unique, Composite, Full-text).
- Unique Index – The unique index feature in SQL database tables enforces uniqueness and maintains data integrity by avoiding data duplication in the table.
- Composite Index – A composite index optimizes and improves table field queries involving multiple columns in SQL database tables.
- Full-text Index – A full-text index in SQL database tables enables fast and efficient table query text search features.
- Clustered Index – This manages the physical storage order of data in the database table and is efficient for data range queries.
- Non-clustered Index – This provides an additional structure for fast table data lookups without modifying the physical order of data in the database table.
- Bitmap Index – This is an efficient method for table column fields with low cardinality, where there are multiple occurrences of a few individual column values.
- Spatial Index – This optimizes table queries for geospatial data in a database table.
- Reverse Key Index – This optimizes performance for table values with auto-increment columns by distributing the index values more evenly in the database table.
