Answers for "whats a primary key"

SQL
4

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 NULL
Posted by: Guest on January-27-2021
1

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
Posted by: Guest on January-07-2021
0

primary key

CREATE TABLE Persons (
    Rollno int NOT NULL,
    FirstName varchar(255),
    LastName varchar(255),
    Age int,
    PRIMARY KEY (ID)
);
Posted by: Guest on July-06-2021

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