Transact sql error message Msg 1779 Level 16 - Table already has a primary key defined on it - means that exists an primary key defined in the table.
Msg 1779 Level 16 Example:
USE model;
GO
CREATE TABLE students( id INT NOT NULL PRIMARY KEY, first_name CHAR(50), last_name CHAR(50),
gender CHAR(1), city CHAR(100), country CHAR(50), dep_id INT);
GO
Invalid alter table:
USE model;
GO
ALTER TABLE students ADD PRIMARY KEY (id) ;
GO
| Message |
|---|
| Msg 1779, Level 16, State 0, Line 1 |
| Table 'students' already has a primary key defined on it. |
| Msg 1750, Level 16, State 0, Line 1 |
| Could not create constraint. See previous errors. |