Differences Between Unique Index and Primary Key
Characteristic |
Unique Index |
Primary Key |
---|---|---|
Basics |
Ensures uniqueness of values in specified column(s), allowing NULL values. |
Uniquely identifies each record in a table and implies non-NULLability. |
Nullable Values |
Allows NULL values in indexed columns. |
Does not allow NULL values in indexed column(s). |
Number of Columns |
Can be applied to one or more columns, enforcing uniqueness across combinations. |
Typically applied to a single column but can join multiple columns (composite primary key). |
Number of Constraints |
Multiple unique indexes can be created on a table for different sets of columns. |
Only one primary key constraint can be defined for a table. |
Purpose |
Ensures data integrity by preventing duplicate values. Used when uniqueness is necessary, but NULL values may exist. |
Serves as a unique identifier for each record and establishes relationships between tables. |
Clustered vs. Non-Clustered |
Can be either clustered or non-clustered, depending on the database engine. |
In many databases, implemented as a clustered index by default, physically ordering rows. |
MySQL Unique Index
In MySQL, a unique index is a crucial tool for ensuring that values in a specific column or a group of columns within a table are unique. This feature is essential to maintain data integrity by preventing duplicate entries where uniqueness is required. In this guide, we’ll explore MySQL’s unique index, covering its syntax, usage, benefits, and important considerations.
Optimizing data integrity and performance is critical in the ever-changing world of database administration. The UNIQUE INDEX is a strong way of doing this. This article will take it through understanding, implementing, and using the UNIQUE INDEX functionality in MySQL databases.