Does "select exists" still return true in my function?

Question

I slightly modified the Select Exists function I found on stackoverflow, but no matter what I try, my function below always returns $sqlResult as true. Even though I only keep two entries in the database. Is Select exists still valid?

None of the answers suggested by the stackoverflow system answered my question, instead suggesting using a method that checks the number of rows returned instead of using exists. (Or the link they gave doesn't really explain what the exists result represents.)

function uniquedoesexist($dbHandle,$tablename,$fieldname,$value) 
{
    $sql = 'SELECT EXISTS(SELECT * FROM `' . $tablename .
         '` WHERE `'.$fieldname.'` = ? 
            LIMIT 1
    )';
    $stmt = mysqli_prepare($dbHandle, $sql);
    mysqli_stmt_bind_param($stmt, 's',$value);  
    $sqlResult = mysqli_stmt_execute($stmt);

    echo '$sqlResult: ' . $sqlResult.$br;
    return $sqlResult;
}

Use: username Index varchar(255) utf8_german2_ci

I'm sorry for my beginner question. Entries for field names are set to be unique.

Answer 1

You need to get the query results in the following way:

function uniquedoesexist($dbHandle, $tablename, $fieldname, $value) {
    $sql = 'SELECT EXISTS(SELECT * FROM `'.$tablename.'` WHERE `'.$fieldname.'` = ? LIMIT 1)';
    $stmt = mysqli_prepare($dbHandle, $sql);
    mysqli_stmt_bind_param($stmt, 's',$value);  
    
    mysqli_stmt_execute($stmt);
    mysqli_stmt_bind_result($stmt, $data);
    mysqli_stmt_fetch($stmt);


    echo "SqlResult for $value: " . $data . PHP_EOL;
    return $data;
}

PHP mysqli online test

Another way is to get the number of rows returned instead of using SELECT EXISTS:

<?php

    function uniquedoesexist($dbHandle, $tablename, $fieldname, $value) {
        
        $sql = 'SELECT * FROM `'.$tablename.'` WHERE `'.$fieldname.'` = ? LIMIT 1;';
        $stmt = mysqli_prepare($dbHandle, $sql);
        mysqli_stmt_bind_param($stmt, 's',$value);  
        
        mysqli_stmt_execute($stmt);
        mysqli_stmt_store_result($stmt);
        
        $found = mysqli_stmt_num_rows($stmt);
    
    
        echo "SqlResult for $value: " . $found . PHP_EOL;
        return $found;
    }

PHP mysqli num_rows