When working with databases, primary keys are essential to uniquely identify each record in a table. But can a table have more than one primary key in SQL? The short answer is no, but let me explain why.
What is a Primary Key?
A primary key is a column or set of columns that uniquely identifies each row in a table. It’s used to enforce data integrity and ensure that each record is distinct.
The Limitation
SQL standards dictate that a table can only have one primary key. This is because a primary key is used to identify each record, and having multiple primary keys would create ambiguity.
Composite Primary Keys
However, there’s a twist. While a table can’t have multiple primary keys, it can have a composite primary key. A composite primary key is a primary key made up of multiple columns. This allows you to use multiple columns to uniquely identify each record.
Why Composite Primary Keys Matter
Composite primary keys are useful when a single column isn’t enough to uniquely identify each record. For example, in a table of students, a composite primary key of ‘Student ID’ and ‘Course ID’ could ensure that each student’s course enrollment is unique.
Conclusion
So, while a table can’t have multiple primary keys in the classical sense, composite primary keys provide a way to use multiple columns to ensure data integrity. It’s essential to understand the difference between these two concepts to design efficient and effective databases.
*Further reading: SQL Primary Key*