If you’re new to relational databases, and you’re trying to get your head around this concept of a “relationship” in your database, I hope this article helps.
Continue readingTag: relationships
Create a Relationship in SQL
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 readingHow to Drop a Foreign Key in SQLite
Normally 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.
Find Foreign Key Violations in SQLite
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.
Return a List of Foreign Keys in SQLite
In SQLite, you can use a PRAGMA statement to return a list of foreign keys for a given table.
Continue readingAdd a Foreign Key to an Existing Table in SQLite
SQLite 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 readingCreate a Foreign Key in SQLite
When 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 readingHow to Enable Foreign Key Support in SQLite
In SQLite, foreign key constraints are not enforced unless foreign key support has been enabled.
Enabling foreign keys involves the following:
- Enable foreign keys when compiling SQLite.
- Enable foreign keys at runtime.
What’s the Difference between a Graph Database and a Relational Database?
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.
Database Tutorial (Part 2) – Relationships, Adding Data, Querying Databases
This article is part 2 of the database tutorial.
Here, we cover:
- Relationships
- The different ways of adding data to a database
- Querying a database