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Relationships: Relationships define how tables within a database are related to each other. Common types
of relationships include one-to-one, one-to-many, and many-to-many. These relationships are established
using foreign keys, which are fields in one table that reference the primary key of another table.
Constraints: Constraints are rules that enforce data integrity within a database. They define the conditions
that must be met for data to be inserted, updated, or deleted in a table. Common types of constraints
include primary key constraints, foreign key constraints, unique constraints, and check constraints.
Degree: This refers to the number of attributes or columns in a table. For example, if a Employee table has
four columns (attributes), then the degree of the table is 4.
Cardinality: This refers to the number of tuples or rows in a table. For example, if a Employee table has
5 rows, then the cardinality of the table is 5.
KEY FIELD
In the LibreOffice Base, data between tables can be related on the basis of a common field called key field.
The key field links the data between two or more tables. LibreOffice Base sets the relationship by comparing
the key fields of tables. Users can specify a link between two tables on the basis of key fields by creating a
relationship.
Primary Key
Primary key is a field that is used to uniquely identify records in a database. It ensures that every row has a
distinct value, preventing duplicates. A primary key cannot contain null values and must be unique. A table
can only have one primary key. If there are more than one field is consider as primary key, then there will be
two identities against a row. But, there can be only one identity against a row. So, we cannot have more than
one primary key. To make the retrieval of records faster, Primary keys are indexed in database.
For example, In the given STUDENT table, the primary key is the STU_ID column as it uniquely identifies
each record.
Table: Student
Primary key Alternate Key
STU_ID S_NAME AADHAR PASSPORT
1 PRIYANKA 1234 A1478
2 ADITI 1254 A1236
3 DEV 1247 A4569
Candidate Key
Candidate Key
An attribute or a set of attributes that can uniquely identify a record and is capable of being a primary key is
called a candidate key. In the Student TABLE, STU_ID, AADHAR, and PASSPORT are the candidate keys as they
have chances of unique values. We can have atleast one candidate key in a table.
Alternate Key
A remaining candidate key that is not selected as the primary key is called an alternate key. In the table
Student, the primary key is STU_ID, and the alternate key is AADHAR and PASSPORT.
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