Filter rows from a relation based on a selection condition.
The Select operation, denoted by the Greek letter sigma (σ), is a fundamental unary operation in relational algebra. Its purpose is to filter the tuples (rows) of a relation, keeping only those that satisfy a specified condition. The result of a Select operation is always a new relation containing a subset of the tuples from the original relation. The format of the operation is σ_p(R), where 'R' is the relation and 'p' is the selection predicate or condition. This predicate is a boolean expression involving the attributes of R, using comparison operators like =, ≠, <, >, ≤, ≥, and logical connectors like AND, OR, and NOT. For example, if we have a 'Students' relation, the operation σ_(major = 'Computer Science')(Students) would produce a new relation containing only the students whose major is 'Computer Science'. The resulting relation will have the exact same schema (set of attributes) as the original 'Students' relation. The Select operation is powerful because it allows us to horizontally partition a table, extracting only the records that are relevant to our query. It corresponds directly to the `WHERE` clause in an SQL query. Understanding the Select operation is the first step in learning how to isolate specific data within a larger dataset.