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

0 vote295 views1 answer
What is SQL data store?
SQL
10 votes285 views1 answer
User_dependencies
SQL
0 vote244 views1 answer
Sql truncate table referencing itself
SQL
0 vote286 views1 answer
Sql query to return field name of a table
SQL
0 vote256 views1 answer
Parsing float to int in mysql
SQL
-1 vote269 views1 answer
Sql getdate date only
SQL
0 vote273 views1 answer
Sql not exists
SQL
0 vote269 views2 answers
Mysql add days to date
SQL
4 votes278 views1 answer
Add constraint fk
SQL
0 vote264 views1 answer
Sql server select ignore dupplicates
SQL