In this topic, we described about the below sections -
What is Alternate Key?
ALTERNATE KEY is a candidate key which consists of one or more columns used to identify each row uniquely which is not treated as a Primary key. If a table contain many candidate keys among them one is treated as Primary key rest of all are called as Alternate keys.
Properties of Alternate Key
- Alternate key does not allow duplicate values.
- Alternate key does not contain NULL values.
- A table may contain more than one Alternate key.
- Alternate key may have more than one column.
- If table consists of only one candidate key. it is treated as Primary key, then there is no Alternate key in that table.
- All Alternate keys are treated as Candidate keys, but All Candidate keys are not Alternate keys because there is a chance of Primary key.
Let us consider below table(s) as an example table(s) to frame the SQL query for getting the desired results.
In above table, emp_id and emp_name are known as candidate keys. By using those two columns, we can get unique value or row from employee_details table. Among of them, one is treated as PRIMARY KEY and another key known as ALTERNATE KEY.