What is primary key

How to make multiple keys as primary in bdms

CREATE TABLE `Donor`(
  `did` int(50) NOT NULL,
  `oid` int(50) NOT NULL,
  `dname` varchar(50) NOT NULL,
  `dblood` varchar(50) NOT NULL,
  PRIMARY KEY (`did`, `oid`)
);

What is primary key

PRIMARY KEY  -- unique identifier for the entire row of record in a table 
             -- can not be null and must be unique

Primary key

CREATE TABLE Persons (
    Rollno int NOT NULL,
    FirstName varchar(255),
    LastName varchar(255),
    Age int,
    PRIMARY KEY (ID)
);

Source: computerscienceai.com

Primary key

Primary Key :
It is unique column in every table in a database
It can ONLY accept;
    - nonduplicate values
    - cannot be NULL

Similar codes

1 vote162 views1 answer
Update from select join
SQL
1 vote194 views1 answer
Too many connections mysql
SQL
6 votes175 views2 answers
Stored procedure to delete data from table in mysql
SQL
4 votes181 views1 answer
SQL find text in SP
SQL
2 votes179 views1 answer
Laravel sql String
SQL
0 vote184 views1 answer
Inserted row count tsql
SQL
0 vote179 views1 answer
Which sql statement would you use to remove a view called emp_dept_vu from your schema?
SQL
2 votes180 views1 answer
Sql like variable
SQL
1 vote195 views1 answer
Mysql curdate between two dates
SQL
0 vote184 views1 answer
Oracle sql developer closed connection
SQL