What is a named query?

Question

I have read its definition but not able to understand fully.

Answer 1

A named query is a SQL expression represented as a table. In a named query, you can specify an SQL expression to select rows and columns returned from one or more tables in one or more data sources. A named query is like any other table in a data source view (DSV) with rows and relationships, except that the named query is based on an expression.

A named query lets you extend the relational schema of existing tables in DSV without modifying the underlying data source. For example, a series of named queries can be used to split up a complex dimension table into smaller, simpler dimension tables for use in database dimensions. A named query can also be used to join multiple database tables from one or more data sources into a single data source view table.

^{(TechNet: Define Named Queries in a Data Source View (Analysis Services))}

@Entity
@Table(name = "users")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "Users.findAll", query = "SELECT u FROM Users u")
    , @NamedQuery(name = "Users.findById", query = "SELECT u FROM Users u WHERE u.id = :id")
    , @NamedQuery(name = "Users.findByUsername", query = "SELECT u FROM Users u WHERE u.username = :username")
    , @NamedQuery(name = "Users.findByPassword", query = "SELECT u FROM Users u WHERE u.password = :password")
    , @NamedQuery(name = "Users.findByStatus", query = "SELECT u FROM Users u WHERE u.status = :status")
    , @NamedQuery(name = "Users.findByDateCreated", query = "SELECT u FROM Users u WHERE u.dateCreated = :dateCreated")})
public class Users implements Serializable {