php/mysql cascading filtering - php

Question

I would like to create some chaining filters that a user can use to narrow down a list of data from the database.
For instance, I have 5 filters types:
by date
by location
by type
by topic
by keyword
The user is free to use all, some or none of these filters at once.
My first impression is that I would have to store a variable with all the "AND's" and "OR's" of my WHERE clause stacked one after the other but it seems tedious as I may have to programmatically add/delete some filter types later.
Is there a way not to use the whole mysql data that I filter once with one huge request but rather chain the targeted requests that I can add/withdraw if necessary?
I mean, can I filter one after the other the result of each previous filtered result?
For instance, instead of doing this:
SELECT * FROM mytable WHERE (A=3 AND B=4 AND ((C>date1) OR (D<date2)) AND D LIKE '%sample%' )
Is it possible to do something that would achieve this idea:
request 1 = SELECT * FROM mytable WHERE A=3
request 2 = SELECT * FROM "result of request 1" WHERE B=4
request 3 = SELECT * FROM "result of request 2" WHERE C>date1 OR D<date2
request 4 = SELECT * FROM "result of request 3" WHERE E LIKE '%sample%'
The first approach is very hard to manage if the filters are meant to change over time while the second approach is just a matter of adding/withdrawing the desired filter to the chain.
Not to mention that the more filters you have, the more the first approach becomes unreadable and unmanageable.
This could be obtained in pure php if I decide to filter the data after retrieving the whole mysql table but is seems counter productive and more verbose while Mysql has all I need to filter the data directly and it seems useless to get the whole data from Mysql when I only need part of it at the end.
Thank you for your help.

Answer 1

I like the first scenario better, I assume you're submitting a form to decide what to filter. The way I would go about making it scalable and easier to read, is just name the form fields the same as your DB fields. Then you can either keep an array containing the fields you want to use, or make a db call to check if a field is one you want to use in the filter. a simple example.
$filterFields = array('startDate'=>'>',
'endDate'=>'<',
'location'=>'=',
'keyword'=>'LIKE');
function buildQuery($filterFields, $mysqli)
{
$partCount = 0;
$query = "SELECT * FROM mytable WHERE ";
foreach($_POST as $key=>$value)
{
//is the field one we want to use? Does it contain a value?
if(in_array($key, array_keys($filterFields) && !empty($value))
{
if($partCount > 1)
$query .= ' AND ';
if($filterFields[$key] == 'LIKE')
$query .= " `".$key."` LIKE '%".mysqli->real_escape_string($value)."%' ";
else
$query .= " `".$key."` ".$filterFields[$key]." '".mysqli->real_escape_string($value)."' ";
++$partCount;
}
}
return $query;
}
Hopefully that makes sense. If that's not doing what you want or you need clarification, let me know. Also this is not tested, just wrote it here.