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 vote190 views1 answer
Selecting Multiple Columns in SQL
SQL
0 vote175 views1 answer
Vbscript clean up ADODB.Recordset
SQL
1 vote171 views1 answer
Mysql show current queries
SQL
2 votes174 views2 answers
How to check data type in sql server
SQL
1 vote171 views1 answer
Last 6 months postgresql
SQL
2 votes183 views1 answer
Merge firstname and lastname in sql oracle
SQL
0 vote125 views1 answer
Oracle sysdba connect as another user
SQL
0 vote163 views1 answer
Mysql return column names when table is empty
SQL
8 votes175 views2 answers
Alert table name mysql
SQL
1 vote194 views1 answer
Illuminate\Database\QueryException SQLSTATE[HY000] [2002] Connection refused (SQL: select * from information_schema.tables where table_schema = laravel and table_name = migrations and table_type = 'BASE TABLE')
SQL