What does a foreign key mean in SQL?

What does a foreign key mean in SQL?

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.

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.

How to avoid create table with foreign key reference?

If you’d like to make sure that the SQL engine won’t insert a row with a foreign key that references a non-existent primary key, then you can add a FOREIGN KEY constraint in your CREATE TABLE statement. You can see the error that it results in by removing the comments from the fourth INSERT in the code below.

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.

Where do I find the foreign key in mytest?

The table contains a PRIMARY KEY CONSTRAINT on ‘cust_code’ and a FOREIGN KEY on ‘agent_code’ without specifying the PRIMARY KEY column – The ‘agent_code’ in ‘agents’ table are unique. Only those ‘agent_code’ which are present in ‘agents’ table will appear in ‘mytest’ table because reference column is ‘agent_code’ of ‘agents’ table.

When do you use the FOREIGN KEY constraint?

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.

When does a foreign key match a primary key?

For each row in the referencing table( the table contains the FOREIGN KEY), the foreign key must match an existing primary key in the referenced table(the table contains the PRIMARY KEY). This enforcement of FOREIGN KEY called the Referential Integrity. The structure and data type of PRIMARY KEY and FOREIGN KEY must be same.

Is the PersonID column in the Orders table a foreign key?

The “PersonID” column in the “Orders” table is a FOREIGN KEY in the “Orders” table. The FOREIGN KEY constraint prevents invalid data from being inserted into the foreign key column, because it has to be one of the values contained in the parent table.

https://www.youtube.com/watch?v=f1oDlHMoWtg