Relationship A primary key’s main features are: It

Relationship types
Relationships
are invisible links between two databases that
a
situation that exists between two relational databases tables when
one table has a foreign key that references the primary key of the
other table. Relationships allow databases to split and store data in
different tables while still being connected.

Benefits
of the relational model of
databases

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The
Advantages of a Relational Database is a database structured on the
“Relational”
model. Data are stored and presented in a tabular format, organized
in rows and columns with one record per row. This
helps a lot having the relational model as there is no duplicated
data and helps a lot with organising tables.

Normalisation

Normalisation is the
process of organizing data in a way that the results make the data
easier for you find individual tables. This also stops data
duplication because you would create a table in between the 2 tables
that have the same data.

Data types
A
data type when
used
in
a
database
is
a way
of
classifying
data into groups of similar things. For example
a
string
is a data type that is used to store
text and an integer is a data type used to classify whole numbers.

Field Sizes
A
term
used to describe the amount of data that can go in 1 field.
All data entry fields have a default maximum size
which
is normally set to 12.
For example a single line input field often has a 255 character limit
while
other things may vary.

Validation rules

A
Validation
rule is a criteria
or constraint used in the database
on a field that limits what the user can type into that field. One a
validation rule is set anything that is not included in it will be
not allowed to enter into
the field.

Primary keys
A
primary key is a special thing
attached to a field that
is
designated
to uniquely identify all table records. A primary key’s main features
are: It must contain a unique value for each row of data. It
is also what you link when linking 2 tables together.
Foreign keys

A
foreign key is a field (or sometimes
a collection
of fields) in one table that uniquely identifies a row of another
table or the same table but
a different position.
The
foreign key is defined in a second table but it refers to the primary
key in the first table.

Referential
integrity
Referential
integrity is a relational only
database
thing
which states that relationships between
tables
must always be consistent. In other words, any foreign key field must
agree with the primary key that is referenced by the foreign key.

Auto incremental keys
Auto-increment
allows a unique number to be generated automatically when a new
record is inserted into a table. Often this is the primary key field
that we would like to be created automatically every time a new
record is inserted. And
example of this is when you are creating character each new character
has there own unique ID number.

Field Attributes
An
attribute in
simple is
a characteristic linked
to a field.
An
attribute refers to a database component, such as a table. It also
may refer to a database field.

Data redundancy
Data
redundancy is a
thing
created within a database in which the same piece of data is held in
two separate places. Whenever
data is repeated, this is
data redundancy. This happens
sometimes happen when your writing lots of data and can occur
by accident but is also done deliberately when
your testing different fields and stuff to check that they work.