Number of bound variables does not match number of tokens PDO - php

Relatively new to PDO (and OOP in general), my 3 named parameters are giving me an error. This is the function I have written to check if a value already exists in the database (so I won't have duplicate entries):
function checkTable($table, $column, $value, $con) {
$stmt = $con->prepare("SELECT * FROM :tbl WHERE :col = :val");
$stmt->execute(['tbl' => $table, 'col' => $column, 'val' => $value]);
return $stmt->fetchAll();
}
Of course $con is the PDO connection (yes I have checked, it is connected and I can run normal queries on the database)
I am calling the function with this piece of code:
checkTable("posts", "title", "title", $con);
I'm expecting to see true being returned, as the value I'm putting in does exist in the database, but all I'm getting is
'SQLSTATE[HY093]: Invalid parameter number: number of bound variables does not match number of tokens'
EDIT: I've tested this outside a function, and this worked just as expected:
$bind = ['tbl' => "posts", 'col' => "title", 'val' => "title"];
$query = query("SELECT * FROM :tbl WHERE :col = :val", $con, $bind);
var_dump($query);
Where the query() function looks like this:
function query($query, $con, $bind = null) {
try {
$stmt = $con->prepare($query);
$stmt->execute($bind);
$stmt->setFetchMode(PDO::FETCH_ASSOC);
$result = $stmt->fetchAll();
return $result;
} catch(Exception $e) {
return false;
}
}

You cannot use table and column names for substitution within prepared statements. :tbl - is a table name. So you have only two tokens in your query :col, :val.
Also :col would be replaced with 'column_name' (with quotes). Where condition would be looks like 'column_name'='value'.

Related

How do I query a database with php using bind variables?

I'm making a song database system, and I'm trying to implement a way for users to search songs based on a category to search (song's name, artist's name, album name, genre etc) and a given search term. To accommodate user input and protect against SQL injection, I'm using a prepared statement made with bind variables, however I'm having trouble with what I currently made:
search("genre", "electropop", $db);
function search($column, $term, $db) {
try {
$sql = "SELECT * FROM Songs WHERE :column=:term;";
$stmt = $db->prepare($sql);
$params = array("column" => $column,
"term" => $term);
$stmt->execute($params);
$arr = $stmt->fetchALL(PDO::FETCH_ASSOC);
print (json_encode($arr));
}
catch(PDOException $ex) {
catch_error("The search failed.", $ex);
}
}
Whenever I test this, I get an empty array back: [ ]
I tested my query ("SELECT * FROM Songs WHERE genre='electropop'") in phpmyadmin and it checks out (gave me back entries).
The correct syntax for WHERE clauses in SQL is that the term needs to be surrounded by quotations (https://www.w3schools.com/sql/sql_where.asp) so I tried escaping quotation marks around the term:
...
$sql = "SELECT * FROM Songs WHERE :column=\':term;\'";
...
But then it fails to even see :term as a token to bind variables to later.
Not sure how to go about solving this. I assumed the empty array is due to a valid search but just no results, but perhaps I'm not correctly using a prepared statement. Any help would be much appreciated! Thanks!
You missed the : before term param. Don't need to bind column name. Just use the $column var instead of :column.
search("genre", "electropop", $db);
function search($column, $term, $db) {
try {
$sql = "SELECT * FROM Songs WHERE $column=:term;";
$stmt = $db->prepare($sql);
$params = array(":term" => $term);
$stmt->execute($params);
$arr = $stmt->fetchALL(PDO::FETCH_ASSOC);
print (json_encode($arr));
}
catch(PDOException $ex) {
catch_error("The search failed.", $ex);
}
}

PDO results are empty

I decided to flip from mysqli/mysqlnd to PDO, however I am encountering a problem I had the last time I did this. I am trying this again as it seems that PDO allegedly supports passing a variable that contains an array of values to the execute() param for binding to the query without having to use things like call_user_func_array.
The code I have for demonstration is :
$bind_arguments[] = "dogs";
$bind_arguments[] = "cats";
$bind_arguments[] = "birds";
$db = new PDO('mysql:dbname=' . SQL_DATA . ';host=' . SQL_SERVER, SQL_USERNAME, SQL_PASSWORD, array (
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
));
$sql = 'SELECT `name` FROM `pets` WHERE `type` = ? OR `type` = ? OR `type` = ?';
$result = Array();
try {
if($stmt = $db->prepare($sql)) {
$stmt->execute($bind_arguments);
$result = $stmt->fetchAll();
}
} catch(PDOException $e) {
echo 'Wrong SQL: ' . $sql . ' Error: ' . $e->getMessage(); exit;
}
$db = null;
var_export($result); // null
I don't get any exceptions, however $result is null. If I do the regular query using Navicat (or using mysqli) It works!
See Example #5, which shows I should be able to do this (posting example from there here for reference) :
<?php
/* Execute a prepared statement using an array of values for an IN clause */
$params = array(1, 21, 63, 171);
/* Create a string for the parameter placeholders filled to the number of params */
$place_holders = implode(',', array_fill(0, count($params), '?'));
/*
This prepares the statement with enough unnamed placeholders for every value
in our $params array. The values of the $params array are then bound to the
placeholders in the prepared statement when the statement is executed.
This is not the same thing as using PDOStatement::bindParam() since this
requires a reference to the variable. PDOStatement::execute() only binds
by value instead.
*/
$sth = $dbh->prepare("SELECT id, name FROM contacts WHERE id IN ($place_holders)");
$sth->execute($params);
?>
Also see Example #1 posted below for convenience :
<?php
$sth = $dbh->prepare("SELECT name, colour FROM fruit");
$sth->execute();
/* Fetch all of the remaining rows in the result set */
print("Fetch all of the remaining rows in the result set:\n");
$result = $sth->fetchAll();
print_r($result);
?>
So why is this not working ? What am I doing wrong ?
Update
I made some typos when posting my code (which was stripped out of a larger class) for StackOverflow's MVCE requirements. These typos were not present in the original class. I have updated them in the code above. - sorry for any confusion this may have caused.
You are assigning values to $bind_array and $bnid_array but are sending in $bind_arguments to execute(). Try changing $bnid_array to $bind_array and use $stmt->execute($bind_array);

PDO : creating a reusable code

I'm trying to create a reusable code in PDO.
here's my code.
$myClass = new main_c();
$condition = "email_address = :email_address AND password = :password";
$array = array('email_address' => 'yiihii#yahoo.com', 'password' => '98467a817e2ff8c8377c1bf085da7138');
$row = $myClass->get('user', $condition, $array, $db);
print_r($row);
Here's my function.
public function get($tablename, $condition, $array, $db){
$stmt = $db->prepare("SELECT * FROM $tablename WHERE $condition");
foreach($array as $k=>$v){
$stmt->bindParam(":$k", $v);
}
try{
$stmt->execute();
}catch(PDOException $e){
$error = new main_c();
echo $error->error_handling($e);
}
return $row=$stmt->fetch(PDO::FETCH_ASSOC);
}
I've tried omitting the AND in the condition and just put a single where clause and it worked. I think there's a problem in the foreach. i'm not sure though.
You are not binding values, but parameters, so in your loop you are only binding one variable $v to key $k. Twice. And by the time you execute your query these variables will contain the values of the last iteration of the loop.
You would need to change bindParam() to bindValue().
However, as you are not using the third parameter of bindParam() / bindValue() - forcing a data type - you can skip that whole loop and do:
try {
$stmt = $db->prepare("SELECT * FROM $tablename WHERE $condition");
$stmt->execute($array);
...

Why doesn't PDO::bindValue() fail in this instance?

I've written the following function to construct and execute an SQL statement with key-value bindings. I'm using bindValue() to bind an array of key-value pairs to their corresponding identifiers in the SQL string. (The echo statements are for debugging).
public function executeSelect($sql, $bindings = FALSE)
{
$stmt = $this->dbPDO->prepare($sql);
if ($bindings)
{
foreach($bindings as $key => $value)
{
$success = $stmt->bindValue($key, $value);
echo "success = $success, key = $key, value = $value<br />";
if (!$success)
{
throw new Exception("Binding failed for (key = $key) & (value = $value)");
}
}
}
echo "Beginning execution<br />";
if ($stmt->execute())
{
return $stmt->fetchAll(PDO::FETCH_ASSOC);
}
else
{
return FALSE;
}
}
The input to this function is as follows:
$stmt = "SELECT * FROM test WHERE id = :id";
$bindings = array(":id" => "3", ":Foo" => "Bar");
On the second loop through the $bindings array, I'd expect $success to evaluate to false, thus throwing the custom Exception since "Bar" cannot be bound to ":Foo", since ":Foo" doesn't exist in the input SQL.
Instead, $success evaluates to true (1) for both key-value pairs in the $bindings array, and a PDOException is thrown by ->execute() "(HY000)SQLSTATE[HY000]: General error: 25 bind or column index out of range"
Why isn't bindValue returning false?
Because it works this way.
it throws an error not at bind but at execute. That's all.
So, there is no need in loop and you can make your method way shorter.
public function executeSelect($sql, $bindings = FALSE)
{
$stmt = $this->dbPDO->prepare($sql);
$stmt->execute($bindings);
return $stmt->fetchAll(PDO::FETCH_ASSOC);
}
There is no need in checking execute result either, I believe.
In case of error it will raise an exception already.
By the way, I'd make several helper functions based on this one, returning scalar value and single row. They are mighty helpful. Though I find named placeholders a bit dull. Compare this code:
$name = $db->getOne("SELECT name FROM users WHERE group=?i AND id=?i",$group,$id);
vs.
$sql = "SELECT name FROM users WHERE group=:group AND id=:id";
$name = $db->getOne($sql,array('group' => $group, 'id' => $id));
named require 2 times more code than anonymous.
A perfect example of WET acronym - "Write Everything Twice"

Is it possible to use mysqli_fetch_object with a prepared statement

All the examples I see using mysqli_fetch_object use mysql_query(), I cannot get it to work with prepared statements. Does anyone know what is wrong with this code snippet, as fetch_object returns null.
$sql = "select 1 from dual";
printf("preparing %s\n", $sql);
$stmt = $link->prepare($sql);
printf("prepare statement %s\n", is_null($stmt) ? "is null" : "created");
$rc = $stmt->execute();
printf("num rows is %d\n", $stmt->num_rows);
$result = $stmt->result_metadata();
printf("result_metadata %s\n", is_null($result) ? "is null" : "exists");
$rc = $result->fetch_object();
printf("fetch object returns %s\n", is_null($rc) ? "NULL" : $rc);
$stmt->close();
The output is:
preparing select 1 from dual
prepare statement created
num rows is 0
result_metadata exists
fetch object returns NULL
This is the code I use to create an object from a prepared statement.
It could perhaps be used in a subclass of mysqli?
$query = "SELECT * FROM category WHERE id = ?";
$stmt = $this->_db->prepare($query);
$value = 1;
$stmt->bind_param("i", $value);
$stmt->execute();
// bind results to named array
$meta = $stmt->result_metadata();
$fields = $meta->fetch_fields();
foreach($fields as $field) {
$result[$field->name] = "";
$resultArray[$field->name] = &$result[$field->name];
}
call_user_func_array(array($stmt, 'bind_result'), $resultArray);
// create object of results and array of objects
while($stmt->fetch()) {
$resultObject = new stdClass();
foreach ($resultArray as $key => $value) {
$resultObject->$key = $value;
}
$rows[] = $resultObject;
}
$stmt->close();
MySql Native Driver extension (mysqlnd), has the get_result method:
$stmt->execute();
$obj = $stmt->get_result()->fetch_object();
I don't believe the interface works like that.
Going by the documentation and examples (http://www.php.net/manual/en/mysqli.prepare.php) it seems that $stmt->execute() does not return a resultset, but a boolean indicating success / failure (http://www.php.net/manual/en/mysqli-stmt.execute.php). To actually get the result, you need to bind variables to the resultset (aftere the execute call) using $stmt->bind_result (http://www.php.net/manual/en/mysqli-stmt.bind-result.php).
After you did all that, you can do repeated calls to $stmt->fetch() () to fill the bound variables with the column values from the current row. I don't see any mention of $stmt->fetch_object() nor do I see how that interface could work with a variable binding scheme like described.
So this is the story for "normal" result fetching from mysqli prepared statments.
In your code, there is something that I suspect is an error, or at least I am not sure you intended to do this.
You line:
$result = $stmt->result_metadata();
assignes the resultset metadata, which is itself represented as a resultset, to the $result variable. According to the doc (http://www.php.net/manual/en/mysqli-stmt.result-metadata.php) you can only use a subset of the methods on these 'special' kinds of resultsets, and fetch_object() is not one of them (at least it is not explicitly listed).
Perhaps it is a bug that fetch_object() is not implemented for these metadata resultsets, perhaps you should file a bug at bugs.mysql.com about that.

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