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What is key in Sql Server?

Keys are fields in a table which participate in below activities in RDBMS systems:
  1. To create relationships between two tables.
  2. To maintain uniqueness in a table.
  3. To keep consistent and valid data in database.
  4. Might help in fast data retrieval by facilitating indexes on column(s).
SQL Server supports various types of keys, which are listed below:
  1. Candidate Key
  2. Primary Key
  3. Unique Key
  4. Alternate Key
  5. Composite Key
  6. Super Key
  7. Foreign Key
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