12
More than one
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2.1.3.1.6 Primary Key
“A
primary
key
is
that
candidate
key
that
will
most
commonly
be
used
to
uniquely
identify a single entity
instance”
[4]. Figure below shows a table called
“tbl_user” with
primary key
user_id.
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Figure 2. 5 Primary Key
2.1.3.1.7 Foreign Key
A foreign
key
is
candidate
key,
located
always
in
child,
always
matches
with
primary
key located in parent entity.
Nonidentifying relationships, as said by Whitten [4], are relationships between 2
entities that none of the primary key attributes is shared. Figure below shows 2 entities
where
in entity
“tbl_purchase_order” has
foreign key
user_id and customer_id.
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