SQL中始终为NULL返回值

Question

I have the following SQL function, and I have delare the $row in the mysqli_stmt_bind_result.

//get the user number per month
public function chartwaitinguservsproduct(){
    $stmt = mysqli_prepare($this->connection, 
            "select 
                (Select COUNT(*)  from reusematching.waitinglist_product) as COUNTP,
                (Select COUNT(*)  from reusematching.waitinglist_user) as COUNTU;
                ");     
    $this->throwExceptionOnError();

    mysqli_stmt_execute($stmt);
    $this->throwExceptionOnError();

    mysqli_stmt_fetch($stmt);
    mysqli_stmt_bind_result($stmt, $row->COUNTP, $row->COUNTU);


    mysqli_stmt_free_result($stmt);
    mysqli_close($this->connection);

    return $rows;

}

but not matter how I change the Database, the $rows always NULL. Why? because of the fetch statement??

Answer 1

Why are you using $row in one place (the bind) and returning $rows ?

Don't you think that might be a bad idea, unless your PHP interpreter is far more advanced than the ones I've seen, and able to automatically associate singular and plural variable names :-)

And, from memory, I think you should probably bind the variables before trying to fetch from them. Again, if your PHP is advanced enough, I suppose it could do some form of temporal manipulation, but I wouldn't bet money on it.

---

Sorry, that's the Australian humour coming through but if you examine the fetch page , it states quite clearly:

Note that all columns must be bound by the application before calling mysqli_stmt_fetch().

I'll assume for now that the row/rows issue was just a typo in your question. If it wasn't, then that will need fixing as well.