DATABASE

2.15. Consider Figure 2.1. In addition to constraints relating the values of columns

in one table to columns in another table, there are also constraints that

impose restrictions on values in a column or a combination of columns

within a table. One such constraint dictates that a column or a group of columns

must be unique across all rows in the table. For example, in the

STUDENT table, the Student_number column must be unique (to prevent two

different students from having the same Student_number). Identify the column

or the group of columns in the other tables that must be unique across

all rows in the table.

Figure 2. STUDENT Schema diagram for Name Student number Class Major the database in Figure 12. COURSE Course name Course number Credit hours Department PREREQUISITE Course number Prerequisite number SECTION Section identifier Course number Semester Year Instructor GRADE REPORT Student number Section identifier Grade Eschema changes are usually needed as the requirements of the database applications change. Most database systems include operations for allowing schema changes. 'tis customary in database parlance to use schemas as the plural for schema, even though schermana is the proper plural form. The word scheme is also sometimes used to refer to a schema