Query work in MySQL workbench but not in PHP

Question

I have rather complex SQL statemens, which are using variables.

The whole block works fine in MySQL workbench.

However, if I want to execute the same code on PHP side, it does not woek.

mysqli_select_db($conn, "$settings_database");
$sql = "
    SET @id := null;

    UPDATE incidents.enrichment
    SET enrichment.ManualEnricher4State = 1
    WHERE ParentTableId = @id :=    (
                                        SELECT * FROM   (
                                                            SELECT enr.ParentTableId
                                                            FROM  incidents.enrichment AS enr
                                                            WHERE enr.ManualEnricher1State Is NULL
                                                            AND (
                                                                    enr.ManualEnricher4State Is NULL 
                                                                        OR 
                                                                    enr.ManualEnricher4State = 2
                                                                )
                                                            LIMIT 1
                                                        ) as x
                                    );
    select @id;
";
$sql = mysqli_query($conn, $sql);
$row = mysqli_fetch_array($sql);
var_dump($row);

Could it for some reason be, that the PHP mysql connector has an issue with variables?

Simple querys work fine...

In this example the result of mysqli_query is simply false...

---

Thanks for the help - meanwhile I have found the solution:

Executing that stuff in single querys and everything works fine...

$sql = "SET @id := null;";
$sql = mysqli_query($conn, $sql);   

$sql = "
    UPDATE incidents.enrichment
    SET enrichment.ManualEnricher4State = 1
    WHERE ParentTableId = @id :=    (
                                        SELECT * FROM   (
                                                            SELECT enr.ParentTableId
                                                            FROM  incidents.enrichment AS enr
                                                            WHERE enr.ManualEnricher1State Is NULL
                                                            AND (
                                                                    enr.ManualEnricher4State Is NULL 
                                                                        OR 
                                                                    enr.ManualEnricher4State = 2
                                                                )
                                                            LIMIT 1
                                                        ) as x
                                    );
";
$sql = mysqli_query($conn, $sql);

$sql = "select @id;";
$sql = mysqli_query($conn, $sql);