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What is primary key and foreign key in SQL with example?
Difference between Primary key and Foreign key
| Primary Key | Foreign Key |
|---|---|
| A primary key constrain is a column or group of columns that uniquely identifies every row in the table of the relational database management system. | Foreign key is a column that creates a relationship between two tables. |
What is a primary key and a foreign key?
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 the use of foreign key in SQL?
The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.
What is a primary key SQL?
The PRIMARY KEY constraint uniquely identifies each record in a table. Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).
What is a foreign key in SQL Server?
A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table. The table containing the foreign key is called the child table, and the table containing the candidate key is called the referenced or parent table.
How is a foreign key different from a primary key?
Foreign Key — A foreign key is just a referential constraint between two tables. If a Primary key is used in the another table then it would be know in the another table as Foreign key which can accept multiple null value. Foreign key always generates after Primary key.
How is the FOREIGN KEY constraint used in MySQL?
The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. 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.
Which is the parent table with the foreign key?
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. Look at the following two tables: