How Should I Store Lists of Related Data in a Relational Database?

Storing Lists in Database Columns: A Guide to Normalized Relational Database Design

Storing hierarchical data, such as lists, in a database column can be a challenge. Let's consider a scenario where you want to store an object FOO that contains a list of fruits, and where fruits are stored in a separate table.

In a normalized relational database, it is not recommended to store a list directly in a column. This creates data integrity issues and makes it difficult to maintain and query the data effectively. Instead, you should create a junction table that relates the FOO object to the fruits.

Designing the Database Schema

Create the following tables:

• FOO: Integer columns for the FOO object attributes.
• Fruits: Integer column for the fruit ID and a character column for the fruit name.
• FOOFruits: This junction table relates FOO objects to fruits. It contains two columns: FruitID and FooID.

Example Schema:

CREATE TABLE FOO (
  id int primary key not null,
  int1 int,
  int2 int,
  int3 int
);

CREATE TABLE Fruits (
  id int primary key not null,
  name varchar(30)
);

CREATE TABLE FOOFruits (
  FruitID int references Fruits (ID),
  FooID int references FOO(id),
  constraint pk_FooFruits primary key (FruitID, FooID)
);

Populating the Data

To add a fruit to the list of a FOO object, insert a row into the FOOFruits table:

INSERT FOOFruits(FooID, FruitID)
SELECT 5, ID FROM Fruits WHERE name = 'Apple';

Advantages of Normalized Design

• Preserves data integrity by ensuring that the fruits in the list are valid.
• Makes it easier to query and manage the data by breaking it down into smaller, related tables.
• Provides flexibility for future changes in the data structure.

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