Is it possible to create a sqlite table with a column having multiple value? - sqlite

Question

For example, Assume i have a table with employee list.
The employee id is the primary key, i have other details of employees such as name, age etc.
The employee can have multiple phone numbers. So, it becomes a multivalued attribute.
We don't know how many phones(contact numbers) the employees has.
Is it possible to have multivalued attribute in sqlite3?
Or is there is any method to accommodate this?
Thanks.

Answer 1

You can accomplish this with following ideas:
create 1 column to store all phone numbers (which makes querying based on numbers difficult, not recommended)
you can create x columns for each number (phone1, phone2, ...) (you need to decide what'll be the maximum number of phone numbers for each user)
You can create separate table for phone numbers and link this table with employee table with foreign key. This allows you to store varying list of phone numbers for each employee (requires new table).
Option 3 seems to be most flexible, however in most cases I've seen there was option 2 implemented (usually people have limited number of phone numbers).

Answer 2

You also could create a serializable custom class to store multiple contact numbers. You can then serialize the custom class into a byte[] and then extract an ASCII string from the byte[]. You'll be able to store this string of multiple contact numbers, but you will have to deserialize the data after reading it back in from the database ( reversing the process below.)
public class Contacts : ISerializable
{
}
if (Contacts is ISerializable)
{
string contactNumbers = String.Empty;
using (var stream = new MemoryStream())
{
var formatter = new BinaryFormatter();
formatter.Serialize(stream, Contacts);
stream.Close();
var bytes = stream.GetBuffer();
contactNumbers = System.Text.Encoding.ASCII.GetString(bytes));
}
//Perform the update for this column or add to your insert query.
}

Answer 3

This is the wrong approach in relational database terms. Instead, you should create a separate table to hold employee phone numbers. The table will have columns employee_id and phone_number. Each employee may have 0 or more records in this table, depending on how many phone numbers you have on file.
You may also want to include a description column so that you can have information about what each phone number is.
Storing multiple values in a single column is a first-order no-no in relational databases. Please don't do it.

Answer 4

Multivalued fields are considered very bad practice in DB Design as it shows a lack of "normal form". Instead you should:
Create a new EmployeePhoneNumber table with 3 columns. EmployeePhoneNumberId, EmployeeId, PhoneNumber and PhoneType.
Add a constraint to restrict the Type column to be one of (Mobile, Home ..).
Now you can add any number of phone numbers, by type, to the new table. query it by employeeId and type, if needed.
This option is not only more flexible but it will save db storage size as you will only allocate storage for phone numbers that actually exist.