PHP，MYSQL：根据其他两个DB字段的结果打印一个DB字段

Question

I need to select two fields from a table in my database, if the two fields aren't empty then I would need to select a new field from the database and print that out into a div class on my page.

I have managed to create a function which should call the two initial fields from my table however cannot figure out how to do the rest.

function returnPlanMoon($val,$con)
{
    return (mysqli_query($con, "SELECT Planet, Moon From MK1 WHERE id = 1"));
}

Eventually I want to be able to check the two initial results and based on the answer select a specific field in the database to be printed.

Answer 1

Calling mysqli_query returns a mysqli_result object, which has a num_rows property. Simply check that $result->num_rows is greater than 0, then run the subsequent query. Depending on the query being run, you might be able to join the queries and skip the second query.

If a result is returned, but either Planet or Moon is/can be empty (null/empty string), you'll need to pull those values from the result and check each one via mysql_fetch_assoc :

if(mysql_num_rows($result) > 0){
    $row = mysql_fetch_assoc($result);
    if(!empty($row['Planet'] and !empty($row['Moon'])){
     //run query here, grab Planet and Moon from $row:
     //mysqli_query($conn, "select foo from bar where Planet={$row['Planet']} and Moon={$row['Moon']}");
    }
}

Answer 2

function returnPlanMoon($val,$con){

    $result (mysqli_query($con, "SELECT Planet, Moon From MK1 WHERE id = $val"));

    $num_rows = mysql_num_rows($result);

    if($num_rows > 0){
       // select a new field from the database and print that out into a div class on my page.
    }

}