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`)
);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 :
It is unique column in every table in a database
It can ONLY accept;
- nonduplicate values
- cannot be NULL
Foreign Key:
It is a column that comes from a different table and
using Foreign key tables are related each other
It is the primary key of another table
It can be duplicate or null for another table
Unique Key:
Only unique value and also can contain NULLprimary key in sql
PRIMARY KEY
-- unique identifier for the entire row of record in a table
-- can not be null and must be uniquewhat is primary key
PRIMARY KEY -- unique identifier for the entire row of record in a table
-- can not be null and must be uniqueprimary key
CREATE TABLE Persons (
Rollno int NOT NULL,
FirstName varchar(255),
LastName varchar(255),
Age int,
PRIMARY KEY (ID)
);primary key
Primary Key :
It is unique column in every table in a database
It can ONLY accept;
- nonduplicate values
- cannot be NULLCopyright © 2021 Codeinu
Forgot your account's password or having trouble logging into your Account? Don't worry, we'll help you to get back your account. Enter your email address and we'll send you a recovery link to reset your password. If you are experiencing problems resetting your password contact us
