Best Data Type for Storing Phone Numbers in SQL Server 2005

• Varchar: This is the recommended data type for phone numbers. Varchar is a variable-length character string, which means it can efficiently store phone numbers of different lengths. Phone numbers can vary depending on country codes, area codes, and local numbers. Varchar allows for this flexibility.

Why not Numeric Types?

• Numeric data types (like int or bigint) are meant for storing numbers used in calculations. Phone numbers have characters like hyphens, spaces, or plus signs that aren't relevant for mathematical operations. Storing them as numeric data types would be inefficient and wouldn't capture these formatting elements.

Indexing for Phone Numbers:

• Indexing can improve search performance in your database. However, it's not always necessary for phone numbers.
  • If you plan to frequently search by phone number, creating an index on the phone number column can speed up those searches.
  • But, if phone number searches are uncommon, an index might not be beneficial and could add overhead to writes (inserting/updating data).

Choosing a Varchar Size:

• When using varchar, you need to specify a maximum length for the data. A common choice is varchar(15) as it can accommodate most phone number formats, including country codes. However, you can adjust this based on your specific needs (e.g., if you know all your phone numbers will be within a certain country).

Enforcing Phone Number Format (Optional):

• You can add a check constraint to your varchar column to ensure only valid characters are entered for phone numbers (digits, hyphens, spaces, plus signs). This helps maintain data integrity.

CREATE TABLE Contacts (
  ContactID int PRIMARY KEY IDENTITY,
  FirstName varchar(50) NOT NULL,
  LastName varchar(50) NOT NULL,
  Phone varchar(15),  -- Allows for most phone number formats
  CONSTRAINT Phone_Format CHECK (Phone LIKE '%[0-9 -+()]%')  -- Optional check for valid characters
);

This code creates a table named "Contacts" with columns for ContactID (primary key with auto-increment), FirstName, LastName, and Phone. The Phone column is a varchar(15) to accommodate most phone number lengths. The optional check constraint ensures only digits, hyphens, spaces, plus signs, and brackets are entered.

Varchar with Specific Size (US Numbers):

CREATE TABLE Customers (
  CustomerID int PRIMARY KEY IDENTITY,
  Name varchar(100) NOT NULL,
  Phone char(10),  -- Fixed length (10 digits) for US numbers only
  CONSTRAINT Phone_US_Format CHECK (LEN(Phone) = 10 AND Phone LIKE '%[0-9]%')
);

This code creates a table named "Customers" with similar columns. However, the Phone column uses char(10) which is ideal for storing phone numbers with a fixed length (like 10 digits for US numbers). The check constraint ensures the length is 10 and only digits are present.

Remember:

• Adjust the data type (varchar/char) and size based on your specific needs.
• Consider adding indexes only if frequent phone number searches are required.

This method involves breaking down the phone number into separate columns for country code, area code, and local number. You can use appropriate data types for each part:

CREATE TABLE Contacts (
  ContactID int PRIMARY KEY IDENTITY,
  FirstName varchar(50) NOT NULL,
  LastName varchar(50) NOT NULL,
  CountryCode char(3),  -- 3 digits for most country codes
  AreaCode char(3),
  LocalNumber char(10),
  CONSTRAINT Phone_Parts_Check CHECK (LEN(CountryCode) = 3 AND LEN(AreaCode) = 3 AND LEN(LocalNumber) = 10)
);

This approach offers more granular control over phone number components and simplifies searches based on specific parts (e.g., area code). However, it requires more storage space and can be less user-friendly when displaying the full phone number.

XML Data Type:

This method uses the XML data type to store the entire phone number along with additional information like extension or phone type (home, mobile).

CREATE TABLE Contacts (
  ContactID int PRIMARY KEY IDENTITY,
  FirstName varchar(50) NOT NULL,
  LastName varchar(50) NOT NULL,
  PhoneData xml
);

You can define an XML schema to structure the phone number information within the XML data. This approach provides flexibility for storing various phone details but requires additional processing and parsing for searching or displaying the phone number.

User-Defined Functions (UDFs):

UDFs allow you to create custom logic for storing and retrieving phone numbers. You can write a UDF to clean and format phone numbers before storing them in a varchar column. Additionally, you can create another UDF to format the stored phone number for display purposes.

This approach offers flexibility and control over phone number handling but requires development effort for creating and maintaining the UDFs.

Choosing the Right Method:

The best method depends on your specific needs. Consider factors like:

• Number of phone numbers per contact: Separate columns might be suitable for multiple phone numbers with different types.
• Search requirements: Separate columns or UDFs could simplify searches based on specific parts.
• Need for additional information: XML is ideal if you need to store phone type or extension.
• Development effort: UDFs require coding expertise, while other methods are simpler to implement.