engelsystem/includes/mysqli_provider.php

<?php
/** @var mysqli $sql_connection */
$sql_connection = null;

/**
 * Close connection.
 *
 * @return bool
 */
function sql_close()
{
    global $sql_connection;

    return $sql_connection->close();
}

/**
 * Return NULL if given value is null.
 *
 * @param mixed $value
 * @return bool
 */
function sql_null($value = null)
{
    return $value == null ? 'NULL' : ("'" . sql_escape($value) . "'");
}

/**
 * Start new transaction.
 *
 * @return mysqli_result|bool
 */
function sql_transaction_start()
{
    global $sql_nested_transaction_level;

    if ($sql_nested_transaction_level++ == 0) {
        return sql_query('BEGIN');
    }

    return true;
}

/**
 * Commit transaction.
 *
 * @return mysqli_result|bool
 */
function sql_transaction_commit()
{
    global $sql_nested_transaction_level;

    if (--$sql_nested_transaction_level == 0) {
        return sql_query('COMMIT');
    }

    return true;
}

/**
 * Stop transaction, revert database.
 *
 * @return mysqli_result|bool
 */
function sql_transaction_rollback()
{
    global $sql_nested_transaction_level;

    if (--$sql_nested_transaction_level == 0) {
        return sql_query('ROLLBACK');
    }

    return true;
}

/**
 * Logs an sql error.
 *
 * @param string $message
 * @return false
 */
function sql_error($message)
{
    // @TODO: Bad idea..
    sql_close();

    $message = trim($message) . "\n";
    $message .= debug_string_backtrace() . "\n";

    error_log('mysql_provider error: ' . $message);

    return false;
}

/**
 * Connect to mysql server.
 *
 * @param string $host    Host
 * @param string $user    Username
 * @param string $pass    Password
 * @param string $db_name DB to select
 * @return mysqli|false The connection handler
 */
function sql_connect($host, $user, $pass, $db_name)
{
    global $sql_connection;

    $sql_connection = new mysqli($host, $user, $pass, $db_name);
    if ($sql_connection->connect_errno) {
        error('Unable to connect to MySQL: ' . $sql_connection->connect_error);
        return sql_error('Unable to connect to MySQL: ' . $sql_connection->connect_error);
    }

    $result = $sql_connection->query('SET CHARACTER SET utf8;');
    if (!$result) {
        return sql_error('Unable to set utf8 character set (' . $sql_connection->errno . ') ' . $sql_connection->error);
    }

    $result = $sql_connection->set_charset('utf8');
    if (!$result) {
        return sql_error('Unable to set utf8 names (' . $sql_connection->errno . ') ' . $sql_connection->error);
    }

    return $sql_connection;
}

/**
 * Change the selected db in current mysql-connection.
 *
 * @param $db_name
 * @return bool true on success, false on error
 */
function sql_select_db($db_name)
{
    global $sql_connection;
    if (!$sql_connection->select_db($db_name)) {
        return sql_error('No database selected.');
    }
    return true;
}

/**
 * MySQL SELECT query
 *
 * @param string $query
 * @return array|false Result array or false on error
 */
function sql_select($query)
{
    global $sql_connection;

    $result = $sql_connection->query($query);
    if ($result) {
        $data = [];
        while ($line = $result->fetch_assoc()) {
            array_push($data, $line);
        }
        return $data;
    }

    return sql_error('MySQL-query error: ' . $query . ' (' . $sql_connection->errno . ') ' . $sql_connection->error);
}

/**
 * MySQL execute a query
 *
 * @param string $query
 * @return mysqli_result|false boolean resource or false on error
 */
function sql_query($query)
{
    global $sql_connection;

    $result = $sql_connection->query($query);
    if ($result) {
        return $result;
    }

    return sql_error('MySQL-query error: ' . $query . ' (' . $sql_connection->errno . ') ' . $sql_connection->error);
}

/**
 * Returns last inserted id.
 *
 * @return int
 */
function sql_id()
{
    global $sql_connection;
    return $sql_connection->insert_id;
}

/**
 * Escape a string for a sql query.
 *
 * @param string $query
 * @return string
 */
function sql_escape($query)
{
    global $sql_connection;
    return $sql_connection->real_escape_string($query);
}

/**
 * Convert a boolean for mysql-queries.
 *
 * @param boolean $boolean
 * @return string
 */
function sql_bool($boolean)
{
    return $boolean == true ? 'TRUE' : 'FALSE';
}

/**
 * Count query result lines.
 *
 * @param string $query
 * @return int Count of result lines
 */
function sql_num_query($query)
{
    return sql_query($query)->num_rows;
}

function sql_select_single_col($query)
{
    $result = sql_select($query);
    return array_map('array_shift', $result);
}

/**
 * @param string $query
 * @return string|null
 */
function sql_select_single_cell($query)
{
    $result = sql_select($query);
    if ($result == false) {
        return null;
    }

    $result = array_shift($result);
    if (!is_array($result)) {
        return null;
    }

    return array_shift($result);
}