MySQL constraint for numeration column

I have situation when a I have to store complex data number in the database. Something like that 21/2011 where 21 is document number, but 2011 is document year. So I need some constraint to handle uniqueness becaus开发者_如何学Pythone there is document with number 21/2010 and 21/2012.

How can I create such constraint when numbering starts each from 1 and there is uniqueness check for complex number value?

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CREATE TABLE documents
        (
        year INT NOT NULL,
        no INT AUTO_INCREMENT,
        PRIMARY KEY (year, no)
        ) ENGINE=MyISAM;

INSERT
INTO    documents(year)
VALUES  (2010),
        (2010),
        (2011);

SELECT  *
FROM    documents;

Unfortunately, the AUTO_INCREMENT part will only work for MyISAM tables, however, uniqueness check will work in InnoDB as well, though you will have to provide the numbers explicitly.

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What is the problem, you can simply create an unique key over these both columns.

An other way would be to store "21/2010" as single varchar column.