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

6 votes348 views1 answer
Check Table Exists
SQL
2 votes371 views1 answer
Removing view
SQL
1 vote354 views1 answer
Moodle query item quiz
SQL
3 votes336 views1 answer
Oracle detect invalid password
SQL
0 vote362 views1 answer
Oracle dynamic select into
SQL
0 vote350 views1 answer
Grepper sql workbench download
SQL
0 vote381 views1 answer
Add week ending date sql server
SQL
23 votes371 views4 answers
How to show all users in mysql
SQL
4 votes338 views1 answer
Create column mysql terminal
SQL
4 votes372 views2 answers
Postgresql default value
SQL