Key difference between SQL Keys

Key difference between SQL Keys

• SQL keys are used to uniquely identify rows in a table.
• SQL keys can either be a single column or a group of columns.
• Super key is a single key or a group of multiple keys that can uniquely identify tuples in a table.
• Super keys can contain redundant attributes that might not be important for identifying tuples.
• Candidate keys are a subset of Super keys. They contain only those attributes which are required to uniquely identify tuples.
• All Candidate keys are Super keys. But the vice-versa is not true.
• Primary key is a Candidate key chosen to uniquely identify tuples in the table.
• Primary key values should be unique and non-null.
• There can be multiple Super keys and Candidate keys in a table, but there can be only one Primary key in a table.
• Alternate keys are those Candidate keys that were not chosen to be the Primary key of the table.
• Composite key is a Candidate key that consists of more than one attribute.
• Foreign key is an attribute which is a Primary key in its parent table but is included as an attribute in the host table.
• Foreign keys may accept non-unique and null values.