Difference Between Primary Key and Unique Key:
What is Primary Key?
A major key (additionally goes by major key phrase), is a singular key in a relational database which identifies every report in a database desk. It’s form of a singular identifier, equivalent to an individual social safety quantity, telephone quantity, driver license quantity, or automobile license plate quantity. A database should have just one major key.
A desk in a database incorporates a column or a set of columns which include values that uniquely determine every row within the desk. This column or a set of columns is known as the first key of the desk which should include distinctive values, and can not include null values. With out a major key, the relational database received’t work.
A major secret’s created by defining a PRIMARY KEY constraint when creating or modifying a desk. Within the SQL Commonplace, a major key could include one or a number of columns, whereas every column is implicitly outlined as NOT NULL. For those who outline a PRIMARY KEY constraint on multiple column, it could lead to duplication of values inside one column, that’s why every mixture of values have to be distinctive for all of the columns.
A primary key has the next features:
- Every desk should have one and just one major key, not multiple.
- A major key can not include NULL values.
- It might include a number of columns.
- All columns have to be outlined as NOT NULL.
- A major secret’s clustered distinctive index by default.
What is Unique Key?
A novel secret’s a set of 1 or multiple column/discipline of a desk that uniquely determine a report in a database desk. The UNIQUE KEY constraint makes certain all of the values in a column are distinctive throughout the database. Similar to a major key, a singular key can even comprise of multiple column. Nevertheless, a singular key can settle for just one null worth. No two rows have the identical values in a database desk.
A novel secret’s fairly much like a major key and will be outlined in the course of the creation of the desk. When a column or a set of columns is marked as distinctive within the relational database system, it checks for integrity of values earlier than assigning the constraint in order that to forestall two data from having equivalent values in a specific column.
UNIQUE is a constraint on a non-PRIMARY KEY column which characterizes the next:
- A UNIQUE KEY constraint ensures the individuality of the values.
- A number of distinctive keys will be outlined on a desk.
- A column could include a NULL worth, however just one NULL worth per column is allowed.
- A novel key could create a non-clustered index by default.
Difference Between Primary Key and Unique Key:
A major secret’s form of a singular key identifier that uniquely identifies a row inside a database desk, whereas a singular key identifies all potential rows that exist in a desk and not simply the at the moment current rows.
A major secret’s used to determine a report in a database desk, whereas a singular secret’s used to forestall duplicate values in a column apart from a null entry.
A major key creates a clustered distinctive index by default whereas a singular secret’s a singular non-clustered index in a database desk by default.
4. Null Values
A major key can not settle for NULL values in a database desk whereas a singular key can settle for just one NULL worth within the desk.
There can solely be one and just one major key on a desk, nevertheless, there will be a number of distinctive keys for a desk in a database system.
Primary Key and Unique Key Comparison Chart:
|A major secret’s used to uniquely determine a report/row in a database desk.||A novel secret’s used to uniquely determine all potential rows in a desk and not solely the at the moment current rows.|
|It doesn’t settle for NULL values.||It could actually settle for just one NULL worth in a desk.|
|It’s clustered index by default which implies knowledge is organized within the clustered index sequence.||It’s a distinctive non-clustered index by default.|
|There will be just one major key in a desk.||A desk can have a number of distinctive keys.|
|Primary secret’s outlined through the use of PRIMARY KEY constraint.||Unique secret’s represented utilizing a UNIQUE constraint.|
|Used to determine a row in a desk.||Used to forestall duplicate values in a column.|
|Primary key values can’t be modified or deleted.||Unique key values will be modified.|
- Each major key and distinctive key are entity integrity constraints which can be related in lots of points. Nevertheless, they’ve their fair proportion of variations relating to programming. Each are important ideas which can be primarily utilized in database administration techniques.
- Primary secret’s a set of a number of columns/fields of a database desk that uniquely determine a report in a desk. Unique key, alternatively, prevents two data from having equivalent values in a column.
- Conceptually, there can solely be one PRIMARY KEY for a given desk, whereas there will be multiple UNIQUE KEY for a desk.
- A major key have to be distinctive however a singular key doesn’t essentially need to be the first key.
- A major key can not settle for NULL values in a desk, whereas a singular key can enable NULL values with an exception of just one NULL in a desk.