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New Perspectives on Microsoft Access 2013, Introductory 1st Edition by Joseph Adamski ,Kathy Finnegan ,Sharon Scollard
Edition 1ISBN: 978-1285099217New Perspectives on Microsoft Access 2013, Introductory 1st Edition by Joseph Adamski ,Kathy Finnegan ,Sharon Scollard
Edition 1ISBN: 978-1285099217 Exercise 1
The
, whose values uniquely identify each record in a table, is called a(n)
, when it is placed in a second table to form a relationship between the two tables.
, whose values uniquely identify each record in a table, is called a(n) , when it is placed in a second table to form a relationship between the two tables.Explanation
Verified
Verified
The primary key , whose values uniquely identify each record in a table, is called a (n) foreign key when it is placed in a second table to form a relationship between the two tables.
Primary key
• Primary key field does not allow repeated and null values.
• Every table must have primary key field. Either the table have one primary key field or more than one primary key field that is called as composite key.
• You can retrieve whole record of a particular row using the primary key field value of that row.
• Access generates a default primary key field which is the ID field with AutoNumber data type.
• A primary key appears as fields in database.
• Primary key field concatenates ID of the parent table with unique ID of another table.
• It is used to differentiate one record from another record in table.
Foreign key
• Foreign key field refers to primary key field in another table.
• This field should also have not null values.
• When you change the data in primary key, it affects the foreign key value in related tables.
• It is used to maintain data integrity.
• The foreign key field values must also appear in primary key of related table to maintain data integrity.
• It is used to manage same person's record in two different tables.
Consider two tables' student and library. Student table consist of fields such as StudID, StudName, and Grade. Library table consist of field such as LibraryCardNo, StudID, and BookName.
Student
Library
Primary key of student table is StudID.
Primary key of library table is LibraryCardNo and foreign key of library table is StudID.
StudID in student table acts as a foreign key in library table. With the help of these keys, you can form relationship between two tables. When you change any StudID number in student table such as 788 instead of 888, these changes will affect in library table's StudID field and 788 are displayed instead of 888 through enforcing relationship between two tables.
Primary key
• Primary key field does not allow repeated and null values.
• Every table must have primary key field. Either the table have one primary key field or more than one primary key field that is called as composite key.
• You can retrieve whole record of a particular row using the primary key field value of that row.
• Access generates a default primary key field which is the ID field with AutoNumber data type.
• A primary key appears as fields in database.
• Primary key field concatenates ID of the parent table with unique ID of another table.
• It is used to differentiate one record from another record in table.
Foreign key
• Foreign key field refers to primary key field in another table.
• This field should also have not null values.
• When you change the data in primary key, it affects the foreign key value in related tables.
• It is used to maintain data integrity.
• The foreign key field values must also appear in primary key of related table to maintain data integrity.
• It is used to manage same person's record in two different tables.
Consider two tables' student and library. Student table consist of fields such as StudID, StudName, and Grade. Library table consist of field such as LibraryCardNo, StudID, and BookName.
Student
Library Primary key of student table is StudID.Primary key of library table is LibraryCardNo and foreign key of library table is StudID.
StudID in student table acts as a foreign key in library table. With the help of these keys, you can form relationship between two tables. When you change any StudID number in student table such as 788 instead of 888, these changes will affect in library table's StudID field and 788 are displayed instead of 888 through enforcing relationship between two tables.
New Perspectives on Microsoft Access 2013, Introductory 1st Edition by Joseph Adamski ,Kathy Finnegan ,Sharon Scollard
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