Page 141 - Computing E-Book Grade 6

The City School 2021-2022

When you design a database, you divide your information into tables, each of
which has a primary key and then add foreign keys to related tables that reference
Handling Databases
those primary keys. These foreign key-primary key pairings form the basis for table
relationships and multi-table queries.

Primary Foreign
Key Key

Relationship
Primary
Key

5.7. Constraints in MS Access

In a database when we define any field as a Primary
Key (PK) there are two rules or constraints applied to

that field automatically. Checkpoint

Not Null: This constraint enforces that this field cannot Databases are structured set
of data.
be left unused. In Database terminology, NOT NULL is Rows are also called records
not considered as empty or zero, it just defined as the whereas columns are called

data has not been entered yet. fields.

Unique: This constraint enforces that the data entered in this field cannot be repeated
or all the values entered should be unique to each other.

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