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 vote140 views1 answer
Mysql select row max date
SQL
1 vote190 views1 answer
Sql oracle update multiple rows
SQL
0 vote161 views2 answers
How to drop mili second in sql
SQL
0 vote150 views1 answer
Get last date join sql
SQL
0 vote169 views1 answer
Sql insert query list of dictionaries
SQL
1 vote110 views1 answer
Import in mysql without a software
SQL
20 votes156 views5 answers
Reset auto increment mysql
SQL
1 vote271 views1 answer
Import sql file from laravel
SQL
3 votes178 views2 answers
Wp do sql query from function
SQL
4 votes193 views2 answers
Mysql alter table set column unique
SQL