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 relationships. It is also represented as1: M relationship. This is the opposite of many to one relationship.
CROW FOOT ERD:
The Crow Foot ERD is an Entity Relationship Diagram which is used to represent the cardinalities present in the basic ER diagram. It is used to represent the relationships present between two tuples or tables present in the database.
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Chapter 3 Solutions
Database Systems: Design, Implementation, & Management
- Modify the CHARTER table to add the attributes shown in the following table. TABLE P8.37 ATTRIBUTES AND VALUES FOR PROBLEM 37 ATTRIBUTE NAME ATTRIBUTE DESCRIPTION ATTRIBUTE TYPE CHAR_WAIT_CHG Waiting charge for each model (copied from the MODEL table) Numeric CHAR_FLT_CHG_HR Flight charge per mile for each model (copied from the MODEL table using the MOD_CHG_MILE attribute) Numeric CHAR_FLT_CHG Flight charge (calculated by CHAR_HOURS_FLOWN CHAR_FLT_CHG_HR) Numeric CHAR_TAX_CHG CHAR_FLT_CHG tax rate (8%) Numeric CHAR_TOT_CHG CHAR_FLT_CHG + CHAR_TAX_CHG Numeric CHAR_PYMT Amount paid by customer Numeric CHAR_BALANCE Balance remaining after payment Numericarrow_forwardCreate a table named REP_CONTRACTS containing the columns listed in the following chart A composite PRIMARY KEY constraint including the Rep_ID, Store_ID, and Quarter columns should be assigned. In addition, FOREIGN KEY constraints should be assigned to both the Rep_ID and Store_ID columns.arrow_forward
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