How do I echo the contents of a MySQL table field? - php

Question

I seem to be having trouble understanding the concept of how to properly use the information in a MySQL database using PHP/MySQLi. As I understand it, you generate a variable representing the connection object:
$connectionObject = mysqli_connect('serverString', 'userString', 'passString', 'databaseString');
then, generate a variable representing the query string you want to use:
$queryString = "SELECT rowName FROM tableName";
then, generate a variable representing the result object returned from a successful query:
$resultObject = mysqli_query($connectionObject, $queryString);
then, you use the fetch_assoc() function to generate an array from the result object and assign it to a variable:
$resultArray = myqli_fetch_assoc($resultObject);
then, you can use a while loop to (I have trouble with this one) to sort through the array and use the content of the row somehow:
while ($resultArray) {
echo $resultArray["rowName"];
}
Do I have this concept the wrong way, somehow, because its just not working for me, even to output the text content of a text-based CHAR(10) field with the contents of no more than: "BLAH".
The need to loop through the array to pick out the array item by name in the end anyway seems moot to me to begin with, but no matter where I look, I find the same concept.
My script code, minus a few key details, is:
if ($connectionObject=mysqli_connect("host0", "username0", "password0", "mysqldatabase0")) {
echo "Con";
}
if ($queryString="SELECT 'testdata' FROM 'testtable'") {
echo "Query";
}
if ($resultObject=mysqli_query($connectionObject, $queryString)) {
echo "Result";
}
if ($resultArray=mysqli_fetch_assoc($resultObject)) {
echo "Array";
}
while ($row=$resultArray) {
echo $row["testdata"];
print_r ($row);
}

Answer 1

mysqli_fetch_assoc returns an associate array of string representing the fetched row in the result set which is your $resultObject.
The problem is where you're using the while loop. You want to capture the returned associative array in a variable and access your data via that variable like follows:
while ($row = $resultArray) {
echo $row["rowName"];
}
To sort by rowName you can use the mysql order by clause in your query like follows which returns your results sorted by rowName:
$queryString = "SELECT rowName FROM tableName order by rowName";
Update after OP posted full code:
In your first if statement what would happen if the connection failed? You want to add some error handling there:
$connectionObject=mysqli_connect("host0", "username0", "password0", "mysqldatabase0"));
if (!$connectionObject) {
// exist out of this script showing the error
die("Error connecting to database " . mysqli_error($connectionObject));
} else {
// Don't really need this else but I'll keep it here since you already had it
echo "Con";
}
The problem is here You are using single quotes for column name and table name which are mysql identifiers. MySQL identifiers quote character is backtick not single quote.
Basically you need to use backticks if one of these identifiers are one of mysql reserved words (MySQL Reserved words), for other cases you don't need to use them.
Update your query:
if ($queryString="SELECT `testdata` FROM `testtable`") {
echo "Query"; // Leaving as is, not required
}
Lastly, an improvement. You want to add error handling here too:
if ($resultObject=mysqli_query($connectionObject, $queryString)) {
echo "Result"; // Leaving as is, not required
} else {
echo "Error executing Query " . mysqli_error($connectionObject);
}
Please note that when you use this script the error messages will be printed at the client i.e. when you use this script in a web application the errors will be shown in the user's browser. So you want to look into implementing logging and not printing them directly.

Answer 2

mysqli_fetch_assoc() returns one row as an associative array, of a mysqli_result object. Each time it is called, it returns the next row of results automatically and when used with a while loop, can be used to fetch an unknown number of result rows.
The $row['columnName'] is used to refer to the column. For example, if you had a person object with columns firstName, lastName, dateOfBirth, you could iterate through each person with a while loop as such:
while($row=mysqli_fetch_assoc($resultObject)){
$fname = $row['firstName'];
$lname = $row['lastName'];
$dob = $row['dateOfBirth'];
echo $fname . ' ' . $lname . ' ' . $dob;
}
This will echo details for a result returning an unknown amount of people.
Remember, calling the
if ($resultArray=mysqli_fetch_assoc($resultObject)) {
echo "Array";
}
before the while loop will skip the first result, so make sure the query returns multiple results when testing, as if you are only providing a resultObject containing one result, this might be why it isn't returning anything.
A better way to check if any results are returned is with the mysqli_num_rows($resultObject) function.
if(mysqli_num_rows($resultObject) > 0){
echo "Array";
}
Also not sure if it was just a typo but just to be sure, in your query you are selecting columnName not rowName:
$queryString = "SELECT columnName1(eg. firstName), columnName2(eg. lastName) FROM tableName";
I just recently started learning PHP, and the mysqli_fetch_assoc function confused me too, so I hope this helps!