Friday, January 13, 2017

PHP and MySQL Basics III -- Resulting Results

In the first two blogs entries on this series we set up a connection to MySQL and sent off a query. Now we need to get the data back from the database and into the application.

An Embarrassment of Riches

PHP has many options for what we want to do. But for the best place to start with was checking that rows were actually returned from a query. Below the results from a query are returned to a variable named $result. We can find out how many rows were returned from the server by examining $result->num_rows.
if (!$result = $mysqli->query($sql)) {
    
    // Again, do not do this on a public site, but we'll show you how
    // to get the error information
    echo "Error: Our query failed to execute and here is why: \n";
    echo "Query: " . $sql . "\n";
    echo "Errno: " . $mysqli->errno . "\n";
    echo "Error: " . $mysqli->error . "\n";
    exit;
}

// succeeded, but do we have a result?
if ($result->num_rows === 0) {
    // Oh, no rows! Sometimes that's expected and okay, sometimes
    // it is not. You decide.
    echo "No data returned.";
    exit;
}

This is a case where a programmer needs to know their data. In some cases you will not have a record or records returned because there is no data. Other times no data returned is a sign of big problems. So you have to have some education on what you expect back, and what you do not expect back.

Example

<?php
$mysqli = new mysqli("localhost", "root", "hidave", "world_x");

/* check connection */
if ($mysqli->connect_errno) {
    printf("Connect failed: %s\n", $mysqli->connect_error);
    exit();
}

/* Select queries return a resultset */
$query="SELECT Name, CountryCode, District FROM city LIMIT 10";

if ($result = $mysqli->query($query)) {

        if ($result->num_rows){
                printf("Select returned %d rows.\n", $result->num_rows);

                /* free result set */
                $result->close();
        } else {
                echo "No data returned";
        }
} else {   // if ($result)
   printf("Query failed: %s", $mysqli_error);
}

$mysqli->close();
?>

Sometime you just need the number of records, like number of outstanding customer orders. But in this case we are making sure we have some data to work with before proceedings.

So Now We Have Data

Now you have at least three choices -- rare, medium, or well done. Err, make that an associative array, an array or an object. Each have their uses and it is okay to have a favorite you use more.
$query="SELECT Name, CountryCode, District FROM city LIMIT 10";

if ($result = $mysqli->query($query)) {

        if ($result->num_rows){
                printf("Select returned %d rows.\n", $result->num_rows);
                $assoc = $result->fetch_assoc();
                $row = $result->fetch_row();
                $obj = $result->fetch_object();
        } else {
                echo "No data returned";
        }
} else {   // if ($result)
   printf("Query failed: %s", $mysqli_error);
}

So you make you choice of method and take the results. Here we use fetch_assoc(), fetch_row(), or fetch_object(). Depending on how you want to refer to the data, you use the one that fits the situation. Of course they are similar in use.

//associated array keys = column name, data = data from DB
printf("Sample assoc array %s -> %s\n", $assoc['Name'], $assoc['CountryCode']);

// simple row
printf("Sample row array %s -> %s\n", $row[0], $row[1]);

//object
printf("Sample object %s -> %s\n", $obj->Name, $obj->CountryCode);

Yes, you need to know all three as you will be looking at old code or someone else code that does not use your favorite. And sometimes you may need an object rather than a simple row.

Full Listing

<?php
$mysqli = new mysqli("localhost", "root", "hidave", "world_x");

/* check connection */
if ($mysqli->connect_errno) {
    printf("Connect failed: %s\n", $mysqli->connect_error);
    exit();
}

/* Select queries return a resultset */
$query="SELECT Name, CountryCode, District FROM city LIMIT 10";

if ($result = $mysqli->query($query)) {

        if ($result->num_rows){
                printf("Select returned %d rows.\n", $result->num_rows);
                $assoc = $result->fetch_assoc();
                $row = $result->fetch_row();
                $obj = $result->fetch_object();
        } else {
                echo "No data returned";
        }
} else {   // if ($result)
   printf("Query failed: %s", $mysqli_error);
}
//associated array keys = column name, data = data from DB
printf("Sample assoc array %s -> %s\n", $assoc['Name'], $assoc['CountryCode']);

// simple row
printf("Sample row array %s -> %s\n", $row[0], $row[1]);

//object
printf("Sample object %s -> %s\n", $obj->Name, $obj->CountryCode);

$result->close();
$mysqli->close();
?>

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