PHP Search system ignore capital letters and add keywords

• Regarding capital letters your question is not very clear. I will assume that the words in the bank are all lowercase and the user types uppercase or lowercase. In this case you just have to use the strtolower function that converts all characters to lowercase

DEMO

$busca = trim($_POST['busca']);
//para remover os espaços duplicados.
$busca = preg_replace('/\s(?=\s)/', '', $busca);
//tudo em minusculas
$busca = strtolower($busca)

//quando uma pessoa digitar umas palavras, elas são explodidas pelo espaço
$exp = explode(" ", $busca); // separando pelo espaço

//e em seguida são implodidas pela | (barra vertical)
$imp = implode("|", $exp); // unindo os valores pela |

//a consulta é como segue
SELECT * FROM pesquisa_clientes WHERE palavraschaves REGEXP '$imp' ORDER BY nome

  

A | (vertical bar) is required for the use of REGEXP, it symbolizes the OR "or", that is, it searches between values separated by | (vertical bar).

To convert accents you can use the function

Function TirarAcento( $texto ) 
{
    $array1 = array(   "á", "à", "â", "ã", "ä", "é", "è", "ê", "ë", "í", "ì", "î", "ï", "ó", "ò", "ô", "õ", "ö", "ú", "ù", "û", "ü", "ç"); 

    $array2 = array(   "a", "a", "a", "a", "a", "e", "e", "e", "e", "i", "i", "i", "i", "o", "o", "o", "o", "o", "u", "u", "u", "u", "c"); 

    return str_replace( $array1, $array2, $texto ); 
}  

 $busca = trim($_POST['busca']);
 $busca = preg_replace('/\s(?=\s)/', '', $busca);

 $busca = strtolower($busca);

 $busca = TirarAcento($busca);
 ............................
 ............................
 ............................

  

call the function TirarAcento after the function strtolower

Want to know why? mouse over the area below yellowish

  

Because the function TirarAcento is doing the change of letters accented only to lowercase, therefore it is indispensable to place the search terms first in lowercase with the function strtolower

On uppercase and lowercase letters, I think the best way is for you to define how you are going to write the words in the bank, if it is a capital letter, for example, when reading the words that the user typed, you transform that string in capital letters with strtoupper string). The second part of the problem, you can break the string that the user typed with the explode, done that, you will have an array with the words captured, then just use the implode and separate the values of the arrays by commas in your select. / p>

It would look something like this:

$busca = trim($_POST['busca']);
//transformo tudo em maiúsculo
$busca = strtoupper($busca)
//quebro a string nos espaços, e gravo no array
$array= explode(" ", $busca)
//where IN (valor1, valor2,valor3), uso o implode para coloca a virgula após cada valor do array
$sql = mysqli_query($conn, "SELECT * FROM pesquisa_clientes WHERE palavraschaves in ('.implode(',', array_map('intval', $array)).') ORDER BY nome");

I do not know if this is working because I have not tried it, but the idea is this