Selection using File scans and Indices
- Now, to select the particular column say CustomerName from the table we will type:
SELECT CustomerName FROM Customer;
- your output will be:
- Also, you can select mutliple values like Customer Name, Age and Country:
SELECT CustomerName,Age FROM Customer;
- your output will be come as:
- Remember, by using * you can select all the attributes of the table:
Select * FROM Customer;
- output is:
Selection Operation in Query Processing in DBMS
Regarding query processing, the term “selection” operation denotes fetching particular rows from a database table that fulfill some given condition or conditions. Why is this important? Because databases manage vast volumes of information, users must be able to narrow down their searches based on different parameters. The next few lines explain how selection works during query processing.
Databases are like huge libraries where information is stored in tables. The “selection” operation is like finding the books you need from all the shelves. It helps you pick out specific rows or records from a table that match certain rules or conditions you set. For example, if you want to find all the books written by a particular author, you would use the selection operation to look through the “Author” column and gather only those rows where the author’s name matches what you searched for. This operation is super important because it allows you to extract just the data you need from the vast amounts of information stored in databases. It’s often combined with other operations like choosing specific columns (projection), combining data from multiple tables (join), and calculating things like sums or averages (aggregation) to create complex database queries.