What is an example alternate key?
An alternate key is a key associated with one or more columns whose values uniquely identify each row in a table, but is not a primary key. For example, if a table’s primary key might be an employee ID, the alternate key might be a combination of the employee’s first, middle, and last name.
What is an alternate key?
An alternate key or secondary key is a key that has not been chosen as the primary key, but is a candidate key. However, it is considered a candidate key for the primary key. A candidate key that is not chosen as the primary key is called an alternate key or a secondary key.
What is an alternate key used for?
Use an alternate key
The alternate key is just a candidate key, so the use/function of the alternate key is the same. This means that the alternate key is also used to identify columns in the table, which can uniquely identify all records in the table.
What do you mean by alternate key in a table, please provide a proper example of an alternate key of a table that contains significant data?
Please provide a relevant example of key candidates from the relevant data table. Answer. Candidate key. A candidate key is a key that can uniquely identify each row in a table. … If there are multiple candidate keys in a table, one of them becomes the primary key and the others are called alternate keys.
What is a candidate key with an example?
Candidate key: The minimum set of attributes that can uniquely identify a tuple is called the candidate key. Example: STUD_NO for STUDENT. The value of the candidate key is unique for each tuple and is not zero. There can be more than one candidate key in a relation.
What is the difference between primary key and alternate key?
Primary key values must be unique and not null. A table can contain multiple superkeys and candidate keys, but a table can only have one primary key. Alternate keys are candidate keys that have not been chosen as the primary key of the table.
Should alternate key values be unique?
Alternative key values must be unique. If the table consists of only one candidate key, it becomes the primary key, there is no alternate key.
When you define the primary key of a table, the DBMS automatically generates a ?
If a table has a primary key defined, the DBMS automatically creates a unique index on the primary key column. Indexes play an important role in the DBMS primary key implementation. When defining the primary key of a table, the DBMS automatically creates a unique index on the declared primary key column.
Which key has more fields?
A composite key is made up of multiple fields to uniquely identify a record.
Can a foreign key be null?
Short answer: Yes, it can be NULL or double. I want to explain why the foreign key must be null, unique or not unique. First, remember that a foreign key simply requires that the value of that field first exists in another table (the parent table). … By definition, zero is not a value.
Is the candidate key the same as the primary key?
A primary key is a unique non-null key that uniquely identifies a record in a table. A table can only have one primary key. A candidate key is also a unique key to uniquely identify a record in a table, but a table can have multiple candidate keys.
