Columns from the subquery cannot be referenced anywhere else in the parent query.The following example demonstrates a non-correlated subquery.
Then this is known as developing an artificial key.
A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains.
You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data.
An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures.
Growth and restructuring of base tables is not reflected in views.