PDO error: SQLSTATE[HY000]: General error: 2031

Question

I'm getting this annoying error and although I have an idea of why I'm getting it, I can't for the life of me find a solution to it.

if ($limit) {
   $sth->bindValue(':page', $page - 1, PDO::PARAM_INT);
   $sth->bindValue(':entries_per_page', $page * $entries_per_page, PDO::PARAM_INT);
}

$sth->execute($criteria);

Query contains placeholders ( :placeholder ). But to add those LIMIT placeholders, I need to use the manual method ( bindValue ) because otherwise the engine will turn them into strings.

I'm not getting the Invalid number of parameters error, so all placeholders have been bound correctly (I assume).

Query:

SELECT `articles`.*, `regional_municipalities`.`name` AS `regional_municipality_name`, 
       `_atc_codes`.`code` AS `atc_code`, `_atc_codes`.`name` AS `substance`
FROM `articles`
LEFT JOIN `_atc_codes`
ON (`_atc_codes`.`id` = `articles`.`atc_code`)
JOIN `regional_municipalities`
ON (`regional_municipalities`.`id` = `articles`.`regional_municipality`)
WHERE TRUE AND `articles`.`strength` = :strength
GROUP BY `articles`.`id`
ORDER BY `articles`.`id`
LIMIT :page, :entries_per_page

All placeholder values reside in $criteria, except for the last two LIMIT, which I manually bind with bindValue() .

Answer 1

This same error 2031 can be issued when one bind two values with the same parameter name, like in:

• $sth->bindValue(':colour', 'blue');
• $sth->bindValue(':colour', 'red');

..so, beware.

Answer 2

You cannot use ->bind* and ->execute($params) . Use either or; if you pass parameters to execute() , those will make PDO forget the parameters already bound via ->bind* .

Answer 3

This exception also appears if you try to run a query with placeholders instead of preparing a statment such as

$stmt = $db->query('SELECT * FROM tbl WHERE ID > ?');

instead of

$stmt = $db->prepare('SELECT * FROM tbl WHERE ID > ?');

Answer 4

From the manual :

public bool PDOStatement::execute ([ array $input_parameters ] )

Execute the prepared statement. If the prepared statement included parameter markers, you must either :

• call PDOStatement::bindParam() to bind PHP variables to the parameter markers: bound variables pass their value as input and receive the output value, if any, of their associated parameter markers

• or pass an array of input-only parameter values

You need to pick a method. You cannot mix both.

Answer 5

It's not exactly an answer, but this error also happens if you try to use a word with a hyphen as placeholders, for example:

$sth->bindValue(':page-1', $page1);

So better use

$sth->bindValue(':page_1', $page1);

Answer 6

This happens if you have mismatching parameters. For example:

$q = $db->prepare("select :a, :b");
$q->execute([":a"=>"a"]);

Answer 7

当您的 SQL 尝试更新 AUTO_INCREMENT 字段时，也会发生异常（至少在 MySQL/PDO 中）。