What are composite keys in SQL and can you give me some examples?

What are composite keys in SQL and can you give me some examples?

Composite keys in SQL are keys that consist of two or more columns used to uniquely identify a row in a table. For example, in a table of orders, you might use both 'order_id' and 'product_id' as a composite key to ensure that each product in an order is uniquely identified.

Can you show me a SQL query that uses a composite key?

Sure! Here's an example query:

CREATE TABLE OrderDetails (
    order_id INT,
    product_id INT,
    quantity INT,
    PRIMARY KEY (order_id, product_id)
);

This creates a table where the combination of 'order_id' and 'product_id' serves as the primary key.

What happens if I try to insert a duplicate composite key?

If you try to insert a duplicate composite key, SQL will return an error indicating that the primary key constraint has been violated, preventing the insertion.

Are there any performance considerations when using composite keys?

Yes, composite keys can impact performance, especially if they involve multiple columns. Indexing strategies should be considered to optimize query performance.