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Introduction
Keys within MySQL are the columns or sets used to create the relationship between greater than two tables. They also serve to retrieve records from the table. Both keys ensure uniqueness to a column or collection of columns within the table or relationship.
The primary difference between the two is that the primary key can identify every record in the table. In contrast, the unique key will not allow duplicate entries in a column, except for null values.
The purpose of this blog is that we’re going to examine the key distinctions between Unique and Primary Keys in relation to different variables. Before making comparisons, we will review the keys in detail.
What is a Primary Key?
A primary key is the minimum list of attributes that can identify any row of a table. The primary key can’t contain a null value. It cannot contain duplicate values.
Primary keys ensure the integrity of the entity type because a row is only one example of the table or entity, the primary key assists in ensuring the integrity of the entity type.
What is a Unique Key?
The term “unique key” refers to a distinct value that safeguards duplicates of values in one table column. The main purpose of a unique value in tables is to avoid duplicate values.
However, the primary key contains unique values when it comes to distinct values. An important distinction makes a unique key distinctive because the one-of-a-kind key can include a null value. However, the primary key doesn’t permit null as a valid value.
What is the Distinction Between Primary Key and Unique Key?
The primary purpose of the key is to ensure entity integrity. On the other hand, the goal of the unique keys is to ensure the use of unique data. Let’s check out more distinctions.
| Point of Difference | Primary Key | Unique Key |
| Function | Primary keys are a kind of unique key identifier which uniquely identifies a particular row in the database table. | A unique key can identify every row that could exist in a table, not only the current rows. |
| Indexing | Primary keys develop a clustered index by default. | A unique key will create a distinct non-clustered database index table by default. |
| Behaviour | The primary key helps identify the record within a table in a database. | In contrast, a distinctive key helps avoid duplicate values within a column with the only exception of an entry that is null. |
| Null Values | A primary key can’t accept null values from tables in databases. | A unique key can accept just one value within the table. |
| Usage of Duplicate Keys | For the primary key, duplicate keys aren’t permitted. | In contrast, in case one or more of the key parts is null, a unique key can use the duplicate keys. |
| Limit | There is one primary key in tables. | There could be multiple distinct keys to the table within databases. |
A single empty or blank string is also permitted to be used in the Unique Key column, and it’s allowed in both string and numeric data type columns. However, in the case of a numeric type column, by default, 0 adds on.
A primary key is a unique key. Every table should have, at the most, one primary key. However, it may contain multiple unique keys. A primary key serves to identify a row of a table. The primary key can’t be null because null isn’t a value.
The Primary key constraint uniquely identifies every record in the table. Primary keys must have distinctive values and cannot include null values.
In this article, we’ve studied the primary and unique keys. We have found the unique key can be beneficial when we need to ensure that the columns do not have duplicate values.
Additionally, the primary key can be helpful when we do not need to maintain null values inside the table. It is also a good option in case there is an external key in another table to establish an inter-table relationship.
