What Can Cause the SQLSTATE[HY000]: General error: 2031 in PDO?

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

This error indicates that there is a problem with the parameters of an SQL query. In this case, it appears that the issue is with the bindValue() method being used to manually add LIMIT placeholders to the query.

The following code is causing the error:

<code class="php">if ($limit) {
   $sth->bindValue(':page', $page - 1, PDO::PARAM_INT);
   $sth->bindValue(':entries_per_page', $page * $entries_per_page, PDO::PARAM_INT);
}</code>

The error occurs because the query contains placeholders (:page and :entries_per_page) that need to be bound using bindValue() before the query can be executed. However, before using bindValue() to bind the LIMIT placeholders, the engine turns them into strings. To fix this issue, you can use the following code:

<code class="php">if ($limit) {
   $query = str_replace(':page', $page - 1, $query);
   $query = str_replace(':entries_per_page', $page * $entries_per_page, $query);
   $sth->execute($criteria);
}</code>

This code will replace the placeholders in the query with their values before executing the query.

Beware of Duplicate Parameter Names

It's important to note that the error 2031 can also be caused by binding two values to the same parameter name. For example:

<code class="php">$sth->bindValue(':colour', 'blue');
$sth->bindValue(':colour', 'red');</code>

Using the same parameter name twice will result in the error. Therefore, it's important to make sure that each parameter name is unique.

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