What is a KEY ?

What is a KEY ?

1. A KEY  is a value used to uniquely identify a record in a table. A KEY could be a single column or combination of multiple columns.
2. key is a single or combination of multiple fields in a table. Its is used to fetch or retrieve records/data-rows from data table according to the condition/requirement. Keys are also used to create relationship among different database tables or views. 

Note: Columns in a table that are NOT used to uniquely identify a record are called non-key columns.