How can I create a CHECK constraint on a VARCHAR column in SQL Server specifying a minimum data length?

问题

I have a VARCHAR(30) column in a Microsoft SQL Server database. I'd like to add a CHECK constraint that does not allow a value in the column to be less than 3 characters. What is the expression I must use?

回答1:

use:

ALTER TABLE [dbo].[YOUR_TABLE]
ADD CONSTRAINT [MinLengthConstraint] CHECK (DATALENGTH([your_column]) > 2)

Reference:

• DATALENGTH vs LEN
• SQL SERVER – 2005 Constraint on VARCHAR(MAX) Field To Limit It Certain Length

来源：https://stackoverflow.com/questions/4426005/how-can-i-create-a-check-constraint-on-a-varchar-column-in-sql-server-specifying