PDO Binding in foreach fails at prepare - php

Question

I would like to create a query that may or may not have more than one part. This means, I will be including an array and looping through it, and appending a query to the main SQL query, then finally prepare it.
First of all, I have defined the sql query
$sql = '';
then, I defined a foreach looping value
$arrayLoopValue = 0;
after that, I have created a foreach loop. In which I increased the arrayLoopValue, appended the sql with a new query based on the array's index.
foreach($questionsArray as $questionAnswerRow){
$arrayLoopValue = $arrayLoopValue + 1;
$sql = $sql .
'INSERT INTO gosurveys_surveys_questions_answers
SET survey_id = :survey_id_' . $arrayLoopValue .
', question_id = :question_id_' . $arrayLoopValue .
', user_email = :user_email_' . $arrayLoopValue .
', answer_type = :answer_type_' . $arrayLoopValue .
', question_answer = :question_answer_' . $arrayLoopValue .
', question_answer_creation_date = UTC_TIMESTAMP(); ';
}
The database / example for this query is NOT important, as all fields match and it's already empty. Only the structure, which is provided above, is required.
This fails at the following line.
$query = $this->conn->prepare($sql);
I tried to echo the query and see if there's something wrong. I got the following output:
INSERT INTO gosurveys_surveys_questions_answers
SET survey_id = :survey_id_1,
question_id = :question_id_1,
user_email = :user_email_1,
answer_type = :answer_type_1,
question_answer = :question_answer_1,
question_answer_creation_date = UTC_TIMESTAMP();
INSERT INTO gosurveys_surveys_questions_answers
SET survey_id = :survey_id_2,
question_id = :question_id_2,
user_email = :user_email_2,
answer_type = :answer_type_2,
question_answer = :question_answer_2,
question_answer_creation_date = UTC_TIMESTAMP();
Which is correct. After this prepare, there's a second foreach loop. But the function does NOT reach after the prepare statement.
I would like to know the reason. MYSQL says the following:
Uncaught exception 'PDOException' with message 'SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'INSERT INTO gosurveys_surveys_questions_answers
SET survey_id = ?, ques'

Answer 1

The name of the parameter is not the important thing.
If you want to run a query more than once then preparing it is a great idea but the parameter names are almost irrelevant. the important thing is the binding of new values to the paramters.
So lets assume this is your query
$sql = "INSERT INTO gosurveys_surveys_questions_answers
SET survey_id = :a,
question_id = :b,
user_email = :c,
answer_type = :d,
question_answer = :e,
question_answer_creation_date = UTC_TIMESTAMP()";
Notice the parameter names are irrelevant as long as they are something unique in the query string.
So now you prepare that query. This passes the basic query to the database where it is compiled and optimized, but is not actually run.
$stmt = $this->conn->prepare($sql);
Now within a loop that gets you the parameter you can run that prepared query 1000, 1,000,000 times if you like, all you have to do is bind new values to the parameters and execute the query, which passes the parameter values to the already prepared (compiled and optimized query) and runs it with the data you pass on the execute()
foreach($inArray as $array) {
// build the array of parameters and values
$params = [ ':a' => $array['field1']
':b' => $array['field2']
':c' => $array['field3']
':d' => $array['field4']
':e' => $array['field5']
];
// execute the prepared query using the new parameters
$stmt->execute($params);
}

Answer 2

here is the way to insert multiple rows of data, you prepare once and insert execute multiple times one prepared statement
$dbh = new PDO($dsn, $user, $pass, $options);
$arrayOfData = [...];
$stmt = $dbh->prepare('INSERT INTO table SET col = :val');
$dbh->beginTransaction();
foreach($arrayOfData as $data) {
$stmt->bindValue(':val', $data);
$stmt->execute();
}
$dbh->commit();

Answer 3

The idea of a prepared statement is that the statement is prepared once and then executed multiple times. Something like this:
$sql = 'INSERT INTO gosurveys_surveys_questions_answers
SET survey_id = :survey_id,
question_id = :question_id,
user_email = :user_email,
answer_type = :answer_type,
question_answer = :question_answer,
question_answer_creation_date = UTC_TIMESTAMP()';
$query = $this->conn->prepare($sql);
foreach($questionsArray as $questionAnswerRow) {
$query->execute([
":survey_id" => $questionAnswerRow["survey_id"],
// etc.
]);
}