如何使用条件过滤器构建MySQL查询？

I'm pretty new to both PHP and MySQL and I'm trying to build a small library of singers' quotes. I'd like the user to be able to search for a quote by typing a part of the quote itself, the singer's name or the singer's band, if any.

Now, that part I pretty much nailed:

$query = 'SELECT * FROM quotes WHERE (quote LIKE "%'.$search_string.'%" OR singerName LIKE "%'.$search_string.'%" OR bandName LIKE "%'.$search_string.'%")';

This works, although it alors returns results where the search_string is in the middle of a word: if I type "her", it will return every quote containing "other" or "together". If I drop the second % from the query, it won't return quotes where the search_string isn't the very first word, which I want it to do.

Anyway, what I'd also like to do is give the possibility to filter the results. Let's say I want the user to be able to only show quotes in English, German or Both, via radio buttons. By default, Both is selected, so the $query above is still valid. However, if the user selects English, it should also say something like AND (language = 'EN').

For now, I tried adding to the query this way:

if ($_POST['language']== "EN") {
  $sql .= " AND (language = 'EN')";
}

It works, but it can be a real hassle, as I also want the user to search for quotes using only the filters, without entering a search query: they would be able to look for quotes in English by singers in Band, for example. So, I also have this:

if (strlen($search_string) < 1) {
  $sql = "SELECT * FROM quotes";
}

But then, the $sql .= " AND (language = 'EN')"; wouldn't be correct anymore, as "AND" should be "WHERE". So I'll have to have another if clause to modify the string, and another one for every filter I decide to apply.

My question is then: how should I build my query, given that there are optional filters, and that the search should also be possible using the filters alone?

Thanks!

Set an always true condition in order to have constant WHERE clause.

$sql = "SELECT * FROM myTable WHERE 1 = 1 "
if (true) {
    $sql .= " AND col1 LIKE '%val%' ";
}