M2 PRIMARY KEYS-The primary key of a relational table uniquely identifies each record in the table. It can either be a normal attribute that is guaranteed to be unique (such as Social Security Number in a table with no more than one record per person) or it can be generated by the DBMS (such as a globally unique identifier, or GUID, in Microsoft SQL Server). Primary keys may consist of a single attribute or multiple attributes in combination.
FOREIGN KEYS-A Foreign Key is a field in a relational table that matches a candidate key of another table. The foreign key can be used to cross-reference tables. For example, say we have two tables, a CUSTOMER table that includes all customer data, and an ORDER table that includes all customer orders. The intention here is that all orders must be associated with a customer that is already in the CUSTOMER table. To do this, we will place a foreign key in the ORDER table and have it relate to the primary key of the CUSTOMER table
REFERENTIAL INTEGRITY-Referential integrity is a database concept that ensures that relationships between tables remain consistent. When one table has a foreign key to another table, the concept of referential integrity states that you may not add a record to the table that contains the foreign key unless there is a corresponding record in the linked table. It also includes the techniques known as cascading update and cascading delete, which ensure that changes made to the linked table are reflected in the primary table.
M2
ReplyDeletePRIMARY KEYS-The primary key of a relational table uniquely identifies each record in the table. It can either be a normal attribute that is guaranteed to be unique (such as Social Security Number in a table with no more than one record per person) or it can be generated by the DBMS (such as a globally unique identifier, or GUID, in Microsoft SQL Server). Primary keys may consist of a single attribute or multiple attributes in combination.
FOREIGN KEYS-A Foreign Key is a field in a relational table that matches a candidate key of another table. The foreign key can be used to cross-reference tables.
For example, say we have two tables, a CUSTOMER table that includes all customer data, and an ORDER table that includes all customer orders. The intention here is that all orders must be associated with a customer that is already in the CUSTOMER table. To do this, we will place a foreign key in the ORDER table and have it relate to the primary key of the CUSTOMER table
REFERENTIAL INTEGRITY-Referential integrity is a database concept that ensures that relationships between tables remain consistent. When one table has a foreign key to another table, the concept of referential integrity states that you may not add a record to the table that contains the foreign key unless there is a corresponding record in the linked table. It also includes the techniques known as cascading update and cascading delete, which ensure that changes made to the linked table are reflected in the primary table.
meant M1 not M2
ReplyDeleteP1 achieved
ReplyDeleteM1 achieved
ReplyDelete