Question

I’ve looked into Dynamic SQL and the inc() function, but neither are really what I’m after.

Say I have a database like this:

grade     name      age
9         Bob       9
10        Sue       11
11        Larry     15
9         Joe       8
10        Carrot    10

I want to create a table that first selects all the rows with the lowest grade (9) then displays the oldest. It then goes through and searches for the next highest grade (10) and displays the oldest. Then goes to the next highest grade (11) and displays the oldest.

I’d like for them all to be in the same table and not have to write out a separate SQL call and different PHP variables for each grade.

This is the SQL call I have right now:

$query = "SELECT * FROM horses WHERE grade='1' ORDER BY points DESC LIMIT 1" or die(mysql_error());

Is there a way I can make the grade column increment until it reaches the highest number in the database?

Thanks for any suggestions.

Answer 1

You don’t need a loop for this if I understand your request. Instead, you need a MAX() aggregate grouped by grade. The following method should work independently of your RDBMS. It relies on a JOIN against a subquery which returns the greatest age per group to get the age/group pair and join that back against the main table to retrieve the name (and other columns as needed).

SELECT
  horses.grade, 
  horses.name, 
  horses.age
FROM
  horses
  JOIN (
    SELECT grade, MAX(age) as maxage
    FROM horses 
    GROUP BY grade
  ) ma ON horses.grade = ma.grade AND horses.age = ma.maxage
ORDER BY grade ASC

Here is an example on SQLFiddle.com

Returns:

GRADE NAME  AGE
9     Bob    9
10    Sue    11
11    Larry  15

It is generally far faster an less resource-intensive to do one query instead of multiple queries in a loop, so this should be the approach whenever possible.