Database Schema

Attributes / Schemas

Across the top of a relation we see attributes; in the following figure, the attributes are title, year, length, and filmType. Attributes of a relation serve as names for the columns of the

Modification of Constraints

It is possible to add, modify, or delete constraints at any time. The way to express such modifications depends on whether the constraint involved is associated with an attribute, a table, or a database schema.

Procedures Stored in the Schema

In this section, we introduce you to a recent SQL standard called Persistent, Stored Modules (SQL/PSM, or just PSM, or PSM-96). Each commercial DBMS offers a way for the user to store with a database schema some functions or procedures that can be used in SQL queries

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