如何构建动态mysql查询以适应所有用户

Question

I need your help with my website search functionality. I'm developing a members area wherein users can search other registered users based on certain criteria, or combination of criteria.

My problem now is how to build a dynamic mysql query to suit the need of each combination of search criteria, where the number of criteria is variable.

Normally, I can write with a pre-determined set of criteria using

   WHERE param1 = '$param1'
   AND param2 = '$param2'
   AND param3 = '$param3'

How do I solve this problem?

Answer 1

If the issue is that you don't know which of the criteria the user will pick, but want to return results for "blank" criteria, you can use the following:

$criteria_1 = $_POST['criteria_1'];
$criteria_2 = $_POST['criteria_2'];
$criteria_3 = $_POST['criteria_3'];

if(!$criteria_1 && !$criteria_2 && !$criteria_1) {

     echo "You must select at least one criteria!";

} else {

   // Run query mentioned below and return results.       

} 

THe query would then look like:

SELECT * from mytable
WHERE
(criteria1 = '$criteria_1' OR '$criteria_1' = '') AND
(criteria2 = '$criteria_2' OR '$criteria_2' = '') AND
(criteria3 = '$criteria_3' OR '$criteria_3' = '')

This will treat any blank (non-selected) parameters as blank and ignore them. Be aware that with the above, if no criteria are given, it will return all results.

Another way to write the above is:

SELECT * from mytable
WHERE
criteria1 IN ('$criteria_1', '') AND
criteria2 IN ('$criteria_2', '') AND
criteria3 IN ('$criteria_3', '')

Again, allowing for no entry at all to return all criteria1 results.