Answers for "primary key foreign key"

SQL
4

foreign key

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


Primary Key :
It is unique column in every table in a database
It can ONLY accept;
    - nonduplicate values
    - cannot be NULL

Unique Key:
Only unique value and also can contain NULL
Posted by: Guest on January-27-2021
0

foreign key constraint

CREATE TABLE Students ( 	 /* Create table with foreign key - Way 1 */
    ID INT NOT NULL
    Name VARCHAR(255)
    LibraryID INT
    PRIMARY KEY (ID)
    FOREIGN KEY (Library_ID) REFERENCES Library(LibraryID)
);

CREATE TABLE Students ( 	 /* Create table with foreign key - Way 2 */
    ID INT NOT NULL PRIMARY KEY
    Name VARCHAR(255)
    LibraryID INT FOREIGN KEY (Library_ID) REFERENCES Library(LibraryID)
);


ALTER TABLE Students 	 /* Add a new foreign key */
ADD FOREIGN KEY (LibraryID)
REFERENCES Library (LibraryID);
Posted by: Guest on July-06-2021
1

what is foreign key

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
Posted by: Guest on January-07-2021
1

What is foreign key?

Foreign Key is a non-key attribute which is derived from the primary key 
of another table which links those tables together.
Posted by: Guest on November-23-2020

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