Alternate Key In Database

If we select registratinno as the primary key then rollno is an alternate key.

Alternate key in database. An alternate key is a function of all candidate keys except the primary key. What is the foreign key. Since we have selected emp id as primary key the remaining key emp number would be called alternative or secondary key. A foreign key is the primary key of one table that is linked with the field of another.

There can be a key apart from primary key in a table that can also be a key. Dba database administrator can choose any of the above key as primary key. This can also be called an alternate key. If there are lots of existing records in a table index creation can be a lengthy process.

Each alternate key has a unique name. Let s take an example of student it can contain name roll no id and class. Is primary key and rest of all columns like name id and class are alternate keys. Nice article apart from the keys mentioned here candidate key primary key foreign key alternate key composite key there are additional keys natural key the key which existed in the real world and is used in business purpose for identifying a record.

This key may or may not be a unique key. Lets say emp id is chosen as primary key. The purpose of foreign keys is to maintain data integrity and allow navigation between two different instances of an entity. You can increase the responsiveness of the customization ui and solution import by doing the index creation as a background process.

If the primary key is on both registrationno and rollno then it represents a composite key. In this example registrationno and rollno are candidate keys. Alternate key is a secondary key it can be simple to understand by an example. The alternate key can be an alternative or a candidate for primary key when needed but it is not the primary key.

Alternate key in sql. In employee table employee phonenumber will have unique values thus it can be used as an alternate key but it is not a primary. A data integration system will use alternate keys to uniquely identify records using one or more entity field values that represent a unique combination. For example to identify an account record with an alternate key you can use the account number or the account number field in combination with some other fields which have values that should not change.

Foreign key is a column that creates a relationship between two tables. Unlike the previous keys we looked at natural surrogate composite an alternate key is a name for existing types of keys and not a new type of key. For example in an employee table empno is a primary key empname is a alternate key that may not be unique but still helps in identifying a row of the table. Unique key back to top a unique key is an attribute in the table which is unique.