Select data depending on dropdown and table

Question

Been scratching my head on this for a while but hopefully someone can guide me:

I have a table (Standards) within my DB that has different foreign keys (Grade, Subject, Branch). On the user side, the user can enter a keyword and can further filter based on Grade (1st-12th) , Subject (Math, English, Science) ,or Branch(depends on Subject selection). This extra filtration is the problem that I am facing. What is a recommended approach for selecting data from the data based on the selections made?

Here is what I have when they don't select to filter the data:

function generalResult($keyword, $connection){

$sql = "SELECT standards_eng.Standard FROM standards_eng  WHERE standards_eng LIKE '%".$keyword."%' ";

$query = $connection->query($sql);

if ($query->num_rows > 0) {
    while ($row = $query->fetch_assoc()) {                     
    echo '<p>' .$row['Standard']. '</p>';
    }
 }
}

Only solution I could come up with was If/else statements but that would be too many to count. For example:

if(Grade!== "" AND SUBJECT == "" AND BRANCH =="") {
//Selects data where Standard is like keyword AND Grade_ID is equal to value selected

} Else if (Grade!== "" AND SUBJECT !== "" AND BRANCH == "") {
//Selects data where Standard is like keyword Grade_ID and Subject is equal to value selected

}Else if{
...
}Else if{...}

Answer 1

I am not completely sure what you want, but if I am correct you want optional filters which can be left empty?

What i would do is create a filter and append/concatenate that string if an extra filter is needed. see underneath for an example.

$filter="WHERE standards_eng LIKE '%".keyword."%'";

if(Grade!==""){
     $filter."AND Grade="value here";
}
if(SUBJECT!==""){
    $filter."AND SUBJECT="value here";
}
if(BRANCH!==""){
    $filter."AND BRACH="value here";
}



$sql = "SELECT standards_eng.Standard FROM standards_eng".$filter;