Here's how I would do it:
By submitting your email address, you agree to receive emails regarding relevant topic offers from TechTarget and its partners. You can withdraw your consent at any time. Contact TechTarget at 275 Grove Street, Newton, MA.
CREATE TABLE twoletters ( code CHAR(2) NOT NULL , CONSTRAINT twoletters CHECK ( CHARACTER_LENGTH(code) = 2 AND SUBSTRING(code FROM 1 FOR 1) BETWEEN 'A' AND 'Z' AND SUBSTRING(code FROM 2 FOR 1) BETWEEN 'A' AND 'Z' ) );
Notice that I chose CHAR(2). This would allow the CHARACTER_LENGTH condition to be omitted, but I left it in if you cannot change your column from VARCHAR.
You may need to change the standard SQL functions (CHARACTER_LENGTH and SUBSTRING) to match your specific database system. For instance, in SQL Server you would use
Dig Deeper on Oracle development languages
Related Q&A from Rudy Limeback
Read about the Mimer Validator, a tool used to verify your SQL code, in this tip from SQL expert Rudy Limeback.continue reading
Read SQL expert Rudy Limeback's advice for counting combinations in a table with SQL's GROUP BY clausecontinue reading
Read an example of an SQL case expression from our SQL expert Rudy Limeback.continue reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.