Example of Foreign Key Constraint

Example: Alternative formulation for 6.3 as a foreign key constraint

ALTER TABLE EXAM_MARK

ADD CONSTRAINT Must_be_enrolled_to_take_exam_alternative3

FOREIGN KEY (StudentId, CourseId)

REFERENCES IS_ENROLLED_ON;

The formulation in Example is available only because the following conditions hold:

• There is a one-to-one correspondence from the specified columns, in the specified order, to those of the primary key of IS_ENROLLED_ON. Corresponding columns do not have to have the same name but they must be of the same declared type. The table name for the referenced table (IS_ENROLLED_ON in the example) can be followed by a commalist of column names in parentheses, in which case that commalist-the referenced columns-must correspond exactly, in the correct order, to some key specified for the referenced table. The referenced columns must be explicitly specified when the applicable key is declared using UNIQUE rather than PRIMARY KEY, or when it is declared using WITHOUT OVERLAPS.

• The referenced table and the referencing table (EXAM_MARK in the example) are both base tables.

Posted Date: 1/18/2013 11:35:54 PM | Location : United States

Ask an Expert

Related Discussions:- Example of foreign key constraint - sql, Assignment Help, Ask Question on Example of foreign key constraint - sql, Get Answer, Expert's Help, Example of foreign key constraint - sql Discussions

Write discussion on Example of foreign key constraint - sql
Your posts are moderated

Write your message here..

Related Questions

Cursors in pl/sql, Cursors The Oracle uses work areas to execute the SQ... Cursors The Oracle uses work areas to execute the SQL statements and to store process information. A PL/SQL construct known as the cursor. Let's you assume name a work area and

Unnest operator in sql, UNNEST operator in SQL The inverse operator of... UNNEST operator in SQL The inverse operator of GROUP is UNGROUP. SQL has an operator, UNNEST, that can be used for similar purposes, but its method of invocation is somewhat p

What are decision support systems, (a) What are decision support systems, a... (a) What are decision support systems, and what role do they play in the business environment? (b) Data warehousing is defined as "a subject-oriented, integrated, non-volatile c

Manipulating individual elements - pl/sql, Manipulating Individual Elements... Manipulating Individual Elements Faraway you have manipulated an entire collection. Within the SQL, to manipulate the individual elements of the collection, and then use the ope

Opening a cursor variable, Opening a Cursor Variable The OPEN-FOR stat... Opening a Cursor Variable The OPEN-FOR statement relates a cursor variable with the multi-row query, executes the query, and then identifies the result set. The syntax for ope

Differentiate between snowflake schema and star schema, Problem: (a) De... Problem: (a) Define the following terms: (i) data mining. (ii) OLAP. (b) Differentiate between snowflake schema and star schema. Support your answer with appropriate

Different locking system in dbms, different lock modes used in the locking ... different lock modes used in the locking system

Data types in sql - timestamp, Data Types in SQL - Timestamp TIMESTAMP... Data Types in SQL - Timestamp TIMESTAMP for values representing points in time on a specified uniform scale. DATE is used for timestamps on a scale of one day, such as DATE '2

Comparison operators- pl/sql, Comparison Operators The Comparison operat... Comparison Operators The Comparison operators can compare one expression to another. The outcome is always true, false, or null. Usually, you use a comparison operators in condi

Perform exception handling with user-defined errors, On occasion, some of B... On occasion, some of Brewbean's customers mistakenly leave an item out of a basket already checked out, so they create a new basket containing the missing items. However, they requ