Projeksjonsspørringer

Projeksjonsspørringer, or projection queries, are a type of database query that retrieves specific attributes or columns from a table rather than entire rows. This is in contrast to selection queries, which filter rows based on certain conditions. The primary purpose of projection queries is to reduce the amount of data returned, making queries more efficient and easier to analyze.

In SQL, projection is achieved using the SELECT statement. For example, a query like SELECT customer_name, email FROM customers would be a projection query, returning only the customer's name and email address, even if the 'customers' table contains many other columns. This is particularly useful when dealing with large datasets, as fetching only necessary data saves bandwidth and processing power.

Projection can also be combined with other query operations like filtering (WHERE clause) and aggregation (GROUP BY clause). For instance, one might project specific columns after filtering for customers in a particular region. The concept of projection is fundamental to relational database management and is a core operation in database querying. It ensures that users receive precisely the information they need without unnecessary data.