How to create a dynamic WHERE clause [duplicate]

Answer 1

Try to build where array

$where = array();


if ((int) $studentID >0) {
   $where[] = " studentID = '{$studentID}' ";
}
if ((int) $QuestionId  >0) {
   $where[] = " QuestionId  = '{$QuestionId }' ";
}

and at end implode $where by AND statment

if (!empty($where)) 
$query['where'] = ' WHERE '. implode(' AND ', $where);

It's only a way. I did not debug this code.

Answer 2

Your cases:

- Student selected != 'All' : Add StudentId = ? in WHERE clause 
- Student selected == 'All' : Remove StudentId = ? from WHERE clause 
- Question selected != 'All' : Add QuestionId = ? in WHERE clause 
- Question selected == 'All' : Remove QuestionId = ? from WHERE clause

<?php
$selectedstudentanswerqry = "WHERE SessionId = ? ";
if ($_POST['student'] != 'All'){
 $selectedstudentanswerqry .= " and StudentId = ? ";
}
else{
/*
$selectedstudentanswerqry .= "
//what is condition for if student == all ?
";
*/
}
if ($_POST['question'] != 'All'){
  $selectedstudentanswerqry .= " and QuestionId = ? ";
}
else{
}
?>

consider that

student = 1 then:

if student != All = true
if question != AA = true

student = All
if student != All = false
if question != AA = true

question = 1 
if student != All = true
if question != AA = true

question = All
if student != All = true
if question != AA = false

check if you want this? I think no.

    //case1
    if ($_POST['student'] != 'All'){
      $selectedstudentanswerqry .= "
      WHERE (SessionId = ? AND StudentId = ?)
      ";
    }

    //case2
    if ($_POST['question'] != 'All'){
      //case 2.1
      if ($_POST['student'] != 'All'){
        $selectedstudentanswerqry .= "
         and  (QuestionId = ?)
        ";
      }
      //case 2.2
      else{
        $selectedstudentanswerqry .= "
        WHERE (SessionId = ? AND QuestionId = ?)
        ";
      }

    }
/*
    testing
    1- student != All, question != All
    case1: true
    case1: result: $selectedstudentanswerqry = WHERE (SessionId = ? AND StudentId = ?)
    case2 : true
    case 2.1: true
    case2.1 result:  $selectedstudentanswerqry .= and  (QuestionId = ?)

    2- student != All question = All
    case1: true
    case1: result: $selectedstudentanswerqry = WHERE (SessionId = ? AND StudentId = ?)
    case2: false

    3- student = All question != All
    case1: false
    case2: true
    case2.1: false
    case2.2: true
    case2.2 result: $selectedstudentanswerqry = WHERE (SessionId = ? AND QuestionId = ?)

    4- student = All question = All
    case1: false
    case2: false
*/