Constraint for phone number in SQL Server

Question

Constraint for phone number to be of 7 digits. How to check if it is of 7 digits in SQL Server?

CREATE TABLE Customer
(
    C_ID INT NOT NULL IDENTITY(1,1) PRIMARY KEY,
    C_Name VARCHAR(255) NOT NULL,
    Phone INT 
);

Answer 1

Do not store phone numbers as integers. Some valid numbers, for instance, could start with a 0 -- if not today, perhaps in the future. To do the validation check, you can use like:

CREATE TABLE Customer (
    C_ID INT NOT NULL IDENTITY(1, 1) PRIMARY KEY,
    C_Name VARCHAR(255) NOT NULL,
    Phone CHAR(7), -- you might not want to have such a precise length
    CONSTRAINT chk_phone CHECK (phone not like '%[^0-9]%') -- check that no number is not a digit 
);

Alternatively, you could write:

CONSTRAINT chk_phone CHECK (phone like '[0-9][0-9][0-9][0-9][0-9][0-9][0-9]') -- check that no number is not a digit