5.3. PRIMARY KEY


  •  The PRIMARY KEY constraint uniquely identifies each record in a table.
  •  Primary keys must contain UNIQUE values, and cannot contain NULL values.
  •  A table can have only one primary key, which may consist of single or multiple fields.
QUERY: - CREATE TABLE employee (e_id int PRIMARY KEY);

  • SQL PRIMARY KEY on ALTER TABLE :-

QUERY: - ALTER TABLE Table_Name ADD primary key (column)

EXAMPLE: - ALTER TABLE employee ADD PRIMARY KEY(e_id);

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