Learning Select from Where Prepared Statements

Learning SELECT FROM WHERE prepared statements

Hello ButterDog let me walk you through PDO step by step.

Step 1)

create a file called connect.php (or what ever you want). This file will be required in each php file that requires database interactions.

Lets start also please note my comments :

?php

//We set up our database configuration
$username="xxxxx"; // Mysql username
$password="xxxxx"; // Mysql password

// Connect to server via PHP Data Object
$dbh = new PDO("mysql:host=xxxxx;dbname=xxxxx", $username, $password); // Construct the PDO variable using $dbh
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); // Set attributes for error reporting very IMPORTANT!
$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, FALSE); // Set this to false so you can allow the actual PDO driver to do all the work, further adding abstraction to your data interactions.
?>

Step 2) Require the connect.php please take a look :

require ('....../........./...../connect.php'); // Require the connect script that made your PDO variable $dbh

Step 3)

to start database interactions just do the following also please read the code comments. For the moment we will not worry about arrays! Get the full gyst of PDO then worry about making it easier to work with! With repetition the "long way" comes more understanding of the code. Do not cut corners to begin with, cut them once you understand what you are doing!

$query = $dbh->prepare("SELECT * FROM note_system WHERE note = :cnote"); // This will call the variable $dbh in the required file setting up your database connection and also preparing the query!

$query->bindParam(':cnote', $cnote); // This is the bread and butter of PDO named binding, this is one of the biggest selling points of PDO! Please remember that now this step will take what ever variable ($cnote) and relate that to (:cnote)

$query->execute(); // This will then take what ever $query is execute aka run a query against the database

$row = $query->fetch(PDO::FETCH_ASSOC); // Use a simple fetch and store the variables in a array

echo $row['yourvalue']; // This will take the variable above (which is a array) and call on 'yourvalue' and then echo it.

Thats all there is to PDO. Hope that helped!

Also take a look at this. That helped me so so much!

I also use this as a reference (sometimes) - The web site looks like crap but there is quality information on PDO on there. I also use this and I swear this is the last link! So after this any questions just ask, but hopefully this can turn into a little reference guide on PDO. (hopefully lol)

Prepared statement for select query

If the query is only run once (per script) and there are indeed no variables in it, it indeed doesn't make much of a difference whether you use prepared statements or a one-off query.

SQL Prepared statements select all result with =

You may use a flexible prepared statement here which will ignore a given column should it be NULL:

$sql = "SELECT *
        FROM crashes_history
        WHERE (region = ? OR ? IS NULL) AND
              (county = ? OR ? IS NULL) AND
              (crash_id = ? OR ? IS NULL)";
$sqlPrepared = $conn->prepare($sql);
$sqlPrepared->bind_param("ssssssii", $region, $region, $county, $county, $crash_id, $crash_id, $limit, $offset);

Select with prepared statements Java

That's not how prepared statements work. Oddly enough, you can't use placeholders for table names. The solution being to use something like:

String sql = String.format("SELECT * FROM %s WHERE name = ?", table);

... and proceed with the rest of your code.

How to use prepared statement for select query in Java?

You need to use:

preparedStatement.executeQuery();

instead of

preparedStatement.executeQuery(login);

when you pass in a string to executeQuery() that query is executed literally and thus the ? is send to the database which then creates the error. By passing query string you are not execution the "cached" prepared statement for which you passed the values.

php mysqli prepared statements select

I told you to limit your select function to a simple primary key lookup. And now you opened a can of worms. As a result you are getting entangled implementation code and unreadable application code.

$table, $args, $sort, $order, $clause

What all these variables are for? How you're going to call this function - a list of gibberish SQL stubs in a random order instead of plain and simple SQL string? And how to designate a list of columns to select? How to use JOINS? SQL functions? Aliases? Why can't you just write a single SQL statement right away? You already have a function for selects, though without this barbaric error reporting code you added to it:

function prepared_query($mysqli, $sql, $params, $types = ""){
    $types = $types ?: str_repeat("s", count($params));
    $stmt = $mysqli->prepare($sql)) { 
    $stmt->bind_param($types, ...$params);
    $stmt->execute();
    return $stmt;
}

Just stick to it and it will serve you all right.

$sql = "SELECT * FROM `teste_table` WHERE id = ? AND username = ?";
$stmt = prepared_query($mysqli, $sql, [$id, $name]);
$row = $stmt->get_result()->fetch_assoc();

The only specific select function could be, again, a simple primary key lookup:

function crud_find($conn, $table, $id)
{
    $table = escape_mysql_identifier($table);
    $sql = "SELECT * FROM $table WHERE id=?";
    $stmt = prepared_query($conn, $sql, [$id], "i");
    return $stmt->get_result()->fetch_assoc();
}

And for the everything else just use a generic function with native SQL.

Is it necessary to use a prepared statement for a select statement without user input?

Necessary, no. Recommended, yes. However the way your query is currently written you get no benefit from the prepared statement. Instead it should be:

mysqli_stmt_prepare($stmt, 
    'SELECT client_account_status FROM version_control WHERE id = ?'));

mysqli_stmt_bind_param($stmt, 'i', 1);
mysqli_stmt_execute($stmt);

The problem with your initial version is that mysql has no way of knowing what part of your query is a parameter and what part is the SQL statement. The point of parameterized queries is to clearly separate the statement from the parameters.

See How can I prevent SQL injection in PHP? for more information on preventing SQL injection.

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