5.2. UNIQUE


  • The UNIQUE constraint ensures that all values in a column are different.
  • Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns.
  • A PRIMARY KEY constraint automatically has a UNIQUE constraint.
  • However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table.

QUERY: - create table company (c_id int primary key identity, c_name nvarchar (25) unique , c_Turnover int);

  • SQL UNIQUE on ALTER TABLE:-

QUERY: - ALTER TABLE Table_Name ADD UNIQUE (column);

EXAMPLE: - ALTER TABLE employee ADD UNIQUE (e_id);

Last modified: Monday, 2 December 2019, 12:17 PM