In SQL, you create a relationship by creating a foreign key constraint.
More specifically, you have a parent table and a child table. The parent contains the primary key, and the child table contains a foreign key that references the primary key of the parent table.
When you use SQL to create a relationship, you can create the relationship at the time you create the table, or you can create it later (by altering the table). This article covers both scenarios.
Continue readingNormally if you need to drop a foreign key in SQL, you’d use the ALTER TABLE statement. But if you’re using SQLite, that’s not an option.
SQLite includes a PRAGMA statement that allows you to check for foreign key violations on a whole database or a given table.
The statement is PRAGMA foreign_key_check, and it works as follows.
In SQLite, you can use a PRAGMA statement to return a list of foreign keys for a given table.
Continue readingSQLite supports a very limited subset of the ALTER TABLE statement. The only things you can do with ALTER TABLE in SQLite is rename a table, rename a column within a table, or add a new column to an existing table.
In other words, you can’t use ALTER TABLE to add a foreign key to an existing table like you can in other database management systems.
Therefore, the only way you can “add” a foreign key to an existing table in SQLite is to create a new table with a foreign key, then transfer the data to the new table.
There’s more than one way to do this, but there is a recommended way.
Continue readingWhen you create a table in SQLite, you can also create a foreign key in order to establish a relationship with another table.
This article provides an example of creating a foreign key when creating a table in SQLite.
Continue readingIn SQLite, foreign key constraints are not enforced unless foreign key support has been enabled.
Enabling foreign keys involves the following:
Graph databases have been gaining popularity over recent years as a viable alternative to the relational model. Graph databases are particularly well suited to storing connected data – data with lots of interconnected relationships, especially those that run many levels deep.
This article looks at the main differences between graph databases and relational databases.
This article is part 2 of the database tutorial.
Here, we cover:
This database tutorial is for beginners. It explains basic concepts and assumes no prior knowledge of databases.
You don’t need to follow along – there aren’t any exercises. But there are plenty of screenshots and a few diagrams. The purpose of the tutorial is to introduce you to the basic concepts of databases.