How to append ORDERBY with where condition in php - php

Question

I am working with mysql and Rest Api in php,I want to use "orderby" according to condition (if "filterId"==3 or 4). In other words:
If I pass filterId='3' then query should be like SELECT ......ORDER by p.sp ASC/DESC
If I pass filterId='4' then query should be like SELECT ......ORDER by m.merchantName ASC/DESC
If I pass both parameters,filterId='3' and filterId='4' then query should be like SELECT ......ORDER by m.merchantName,p.sp ASC/DESC
If not pass filterId='3' or filterId='4' then orderby not apply/append
How can I do this? Here is my current code:
if(isset($_GET["Filter"]))
{
$filter=trim($_GET['Filter']);
$data=json_decode($filter);
// echo "<pre>";print_R($data);
foreach($data as $dt)
{
foreach($dt as $d)
{
//echo $d->filter_id;
if($d->filter_id=="1")
{
}
if($d->filter_id=="3")
{
}
}
}

Answer 1

Try this.
$query = "Select * from .... ORDER BY";
if(isset($_GET["Filter"]))
{
$filter=trim($_GET['Filter']);
$data=json_decode($filter);
// echo "<pre>";print_R($data);
foreach($data as $dt)
{
foreach($dt as $d)
{
//echo $d->filter_id;
if($d->filter_id=="1")
{
$query .='ORDER BY p.asp';
}
else if($d->filter_id=="3")
{
$query .='ORDER BY m.merchantName';
}
else
{
break;
}
}
}
For your third condition, you might have to use in_array_all() as below:
function in_array_all($lookfor, $mainarray) {
return empty(array_diff($lookfor, $mainarray));
}

Answer 2

//Try this
$query = 'select * from ...';
$order_by_clause = '';
if(isset($_GET["Filter"]))
{
$filter=trim($_GET['Filter']);
$data=json_decode($filter);
foreach($data as $dt)
{
foreach($dt as $d)
{
//echo $d->filter_id;
if($d->filter_id=="3")
{
$order_by_clause = 'ORDER BY p.sp ASC';
}
else if($d->filter_id=="4")
{
$order_by_clause = 'ORDER BY m.merchantName';
}
else if(($d->filter_id=="3") && if($d->filter_id=="4"))
{
$order_by_clause = 'ORDER BY m.merchantName,p.sp';
}
else if(!(($d->filter_id!="3") || if($d->filter_id!="4"))
{
$order_by_clause = '';
}
}
}
}
$query .= $order_by_clause;