MySQL Primary and Foreign Keys

The primary key can be any field or column of a table, which should be a unique and non-null value for each record or a row. The Foreign key is a field that contains the primary key of some other table to establish a connection between each other.

1. What is primary key and foreign key in MySQL?
2. What is the difference between primary key and foreign key?
3. How can use primary key and foreign key in MySQL with example?
4. How link two tables with primary and foreign key in MySQL?
5. Can a primary key be a foreign key?
6. Can foreign key be null?
7. What data type is a primary key?
8. What is primary key and foreign key with example?
9. What is primary key foreign key unique key?
10. What are primary and foreign keys?
11. What is a foreign key example?
12. How do you insert a foreign key?

What is primary key and foreign key in MySQL?

A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table. The table with the foreign key is called the child table, and the table with the primary key is called the referenced or parent table.

What is the difference between primary key and foreign key?

Primary key is used to identify data uniquely therefore two rows can't have the same primary key. It can't be null. On the other hand, foreign key is used to maintain relationship between two tables. Primary of a table act as forgein key in the other table.

How can use primary key and foreign key in MySQL with example?

Primary and Foreign Key in SQL With Examples

1. CREATE TABLE tableName ( col1 int NOT NULL, col2 varchar(50) NOT NULL, col3 int, ...
2. CREATE TABLE childTable ( col1 int NOT NULL, col2 int NOT NULL, col3 int, ...
3. CREATE TABLE DataFlair( emp_id varchar(5) NOT NULL, name varchar(50), ...
4. CREATE TABLE location( location_id varchar(5) NOT NULL, location varchar(50) NOT NULL,

How link two tables with primary and foreign key in MySQL?

SQL join two tables related by a single column primary key or foreign key pair using where clause

1. ' company_id' is primary key in 'company' table,
2. ' company_id' is foreign key in 'foods' table which is referencing to the, primary key of 'company' table,
3. ' company_id' of 'company' and 'foods' must be same,
4. '

Can a primary key be a foreign key?

Foreign keys are almost always “Allow Duplicates,” which would make them unsuitable as Primary Keys. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship.

Can foreign key be null?

Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table). ... Null by definition is not a value.

What data type is a primary key?

A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values. A table can have only one primary key, which may consist of single or multiple fields.

What is primary key and foreign key with example?

Difference Between Primary key & Foreign key

What is primary key foreign key unique key?

A primary key of one table can be referenced by foreign key of another table. ... Unique key constraints also identifies an individual tuple uniquely in a relation or table. A table can have more than one unique key unlike primary key. Unique key constraints can accept only one NULL value for column.

What are primary and foreign keys?

A primary key is a column or a set of columns in a table whose values uniquely identify a row in the table. ... A foreign key is a column or a set of columns in a table whose values correspond to the values of the primary key in another table.

What is a foreign key example?

Definition: Foreign keys are the columns of a table that points to the primary key of another table. They act as a cross-reference between tables. For example: In the below example the Stu_Id column in Course_enrollment table is a foreign key as it points to the primary key of the Student table.

How do you insert a foreign key?

If you are inserting data into a dependent table with foreign keys:

1. Each non-null value you insert into a foreign key column must be equal to some value in the corresponding parent key of the parent table.
2. If any column in the foreign key is null, the entire foreign key is considered null.