MySQL: How to get a sequential number with rows?

Question

How can I number my results where the lowest ID is #1 and the highest ID is the #numberOfResults

Example: If I have a table with only 3 rows in it. whose ID's are 24, 87, 112 it would pull like this:

ID  24  87  112
Num 1   2   3

The reason why I want this, is my manager wants items to be numbered like item1, item2, etc. I initially made it so it used the ID but he saw them like item24, item87, item112. He didn't like that at all and wants them to be like item1, item2, item3. I personally think this is going to lead to problems because if you are deleting and adding items, then item2 will not always refer to the same thing and may cause confusion for the users. So if anyone has a better idea I would like to hear it.

Thanks.

Answer 1

I agree with the comments about not using a numbering scheme like this if the numbers are going to be used for anything other than a simple ordered display of items with numbers. If the numbers are actually going to be tied to something, then this is a really bad idea!

Use a variable, and increment it in the SELECT statement:

SELECT
    id,
    (@row:=@row+1) AS row
FROM table,
(SELECT @row:=0) AS row_count;

Example:

CREATE TABLE `table1` (
    `id` int(11) NOT NULL auto_increment,
    PRIMARY KEY  (`id`)
) ENGINE=InnoDB

INSERT INTO table1 VALUES (24), (87), (112);

SELECT
    id,
    (@row:=@row+1) AS row
FROM table1,
(SELECT @row:=0) AS row_count;

+-----+------+
| id  | row  |
+-----+------+
|  24 |    1 |
|  87 |    2 |
| 112 |    3 |
+-----+------+

How it works

@row is a user defined variable. It is necessary to set it to zero before the main SELECT statement runs. This can be done like this:

SELECT @row:=0;

or like this:

SET @row:=0

But it is handy to tie the two statements together. This can be done by creating a derived table, which is what happens here:

FROM table,
(SELECT @row:=0) AS row_count;

The the second SELECT actually gets run first. Once that's done, it's just a case of incrementing the value of @row for every row retrieved:

@row:=@row+1

The @row value is incremented every time a row is retrieved. It will always generate a sequential list of numbers, no matter what order the rows are accessed. So it's handy for some things, and dangerous for other things...

Answer 2

Sounds like it would be better just making that number in your code instead of trying to come up with some sort of convoluted way of doing it using SQL. When looping through your elements, just maintain the sequentiality there.

Answer 3

What is the ID being used for?

If it's only for quick and easy reference then that's fine, but if it's to be used for deleting or managing in any way as you mentioned then your only option would be to assign a new ID column that is unique for each row in the table. Doing this is pointless though because that duplicates the purpose of your initial ID column.

Answer 4

My company had a similar challenge on a CMS system that used an order field to sort the articles on the front page of the site. The users wanted a "promote, demote" icon that they could click that would move an article up or down.

Again, not ideal, but the strategy we used was to build a promote function and accompanying demote function that identified the current sort value via query, added or subtracted one from the previous or next value, respectively, then set the value of the initially promoted/demoted item. It was also vital to engineer the record insert to accurately set the initial value of newly added records so inserts wouldn't cause a duplicate value to be added. This was also enforced at the DB level for safety's sake. The user was never allowed to directly key in the value of the sort, only promote or demote via icons. To be honest, it worked quite well for the user.

If you have to go this route.....it's not impossible. But there is brain damage involved....