Primary Key:
A Primary Key in a
Example:
- Students in Universities are assigned a unique registration number.
- Therefore, in a STUDENT database table, the attribute “reg_no” acts as primary key.
Foreign Key:
Foreign Key is a column in a relational database table which provides a relation between two tables. It provides a cross reference between tables by pointing to primary key of another table.
Example:
- In STUDENT database table, the attribute “reg_no” acts as primary key and in COURSE database table in which the student selects his or her course, the same “reg_no” acts as foreign key for the STUDENT table.
Many to One Relationship:
When more than one record in a database table is associated with only one record in another table, the relationship between the two tables is referred as many to one relationship. It is also represented as M: 1 relationship.
One to Many Relationships:
When one record in a database table is associated with more than one record in another table, the relationship between the two tables is referred as one-to-many relationship. It is also represented as1: M relationship. This is the opposite of many to one relationship.
RELATIONAL DIAGRAM:
Relational Diagram is also known as Entity Relational Diagram. It is used to define the conceptual view of the database as viewed by the end user. It is used to depict the database’s main components: entities, relationships and attributes. It describes how data is related to each other.
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Chapter 3 Solutions
Database Systems: Design, Implementation, & Management
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- For each table, identify the primary key and the foreign key(s). If a table does not have a foreign key, write None. FIGURE P3.17 THE CH03_TRANSCO DATABASE TABLESarrow_forwardAn EMPLOYEES table was added to the JustLee Books database to track employee information. Display a list of each employee’s name, job title, and manager’s name. Use column aliases to clearly identify employee and manager name values. Include all employees in the list and sort by manager name.arrow_forwardUsing the tables in Figure Q3.13, create the table that results from MACHINE DIFFERENCE BOOTH. FIGURE Q3.13 THE CH03_VENDINGCO DATABASE TABLESarrow_forward
- Use Figure Q3.13 to answer Questions 1317. FIGURE Q3.13 THE CH03_VENDINGCO DATABASE TABLES Write the relational algebra formula to apply a UNION relational operator to the tables shown in Figure Q3.13.arrow_forwardWrite the SQL code to calculate the ASSIGN_CHARGE values in the ASSIGNMENT table in the Ch07_ConstructCo database. (See Figure P7.1.) Note that ASSIGN_CHARGE is a derived attribute that is calculated by multiplying ASSIGN_CHG_HR by ASSIGN_HOURS.arrow_forwardProblem 1 and 2 are based on the following query: SELECT EMP_LNAME, EMP_FNAME, EMP_AREACODE, EMP_SEX FROM EMPLOYEE WHERE EMP_SEX = 'F' AND EMP_AREACODE = '615' ORDER BY EMP_LNAME, EMP_FNAME; What indexes should you create? Write the required SQL commands.arrow_forward
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