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Languages :: PHP :: Unique numbers
By: krism U.S.A.  Date: 19/09/2004 00:00:00  English  Points: 20 Status: Answered
Quality : Excellent
Hi everyone


I have created an online booking form for a sports hall, the problem that I am having is each booking must have a unique number between 000 and 999. I have no idea how i can get the next availbe number from the database is there is one. If any one can help it would be much apreciated.

Thanks in advance
By: VGR Date: 19/09/2004 23:19:00 English  Type : Answer
SELECT MAX(id) FROM tablename;

I suggest having id integer unique auto_increment,althought this will not auto-limit it to 999
By: generalk Date: 20/09/2004 00:18:00 English  Type : Comment
Since you have a limited range of numbers, you might want to keep a special table of available numbers. In mySql it would look something like this. Other databases will be similar:

CREATE TABLE available_numbers (
free_number INTEGER NOT NULL
);

Whenever a new number comes available (somebody logs out, a bookig in cancelled, etc) do this:

INSERT available_numbers VALUES ($freeed_number)

then, to net the next available number, do this:

SELECT (@x:=free_number) AS next FROM available_numbers LIMIT 1;

and make sure to take it out of the table, like this:

DELETE FROM available_numbers WHERE free_number = @x;
By: T-Dob Date: 20/09/2004 00:58:00 English  Type : Comment
If the purpose is to add one more record in your database, you should better use the AUTO_INCREMENT feature of MySQL. Then, if to insert a new element, your specify all needed field except the id that will be automatically set to the next one.

ref: <A HREF="http://www.mysql.com/doc/en/example-AUTO_INCREMENT.html">http://www.mysql.com/doc/en/example-AUTO_INCREMENT.html</A>
By: wise0ne Date: 21/09/2004 17:53:00 English  Type : Comment
CREATE TABLE book (
uid int(3) NOT NULL auto_increment,
title varchar(60) default NULL,
author varchar(60) default NULL,
UNIQUE KEY uid (uid)
) TYPE=MyISAM;


Inserting data 2 table
INSERT INTO `book` (`uid`, `title`, `author`) VALUES (NULL, 'ABC', 'DEF');

when u giv NULL to uid it will auto_increment the value so u will get unique number all the time. Guess this solved ur problem

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