How to Resolve PDO Parameter Binding Error: \"SQLSTATE[HY000]: General Error: 2031\"?

PDO Parameter Binding Error: SQLSTATE[HY000]: General Error 2031

When utilizing PHP's PDO library, you may encounter the frustrating error "PDO error: SQLSTATE[HY000]: General error: 2031." This error is indicative of an issue with parameter binding.

One potential cause of this error is binding multiple values to a single parameter name. Consider the following example:

<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>

In this code, the bindValue() method is used to manually bind two values to the ':page' parameter. This is necessary because the PDO engine will convert placeholders (:placeholder) into strings if you attempt to use them directly in the LIMIT clause.

However, binding multiple values to the same parameter name is incorrect and will result in the "SQLSTATE[HY000]: General error: 2031" error.

Solution:

To resolve this error, ensure that each parameter name is used only once for binding. In your example, you should declare separate parameters for the ':page' and ':entries_per_page' values. For instance:

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

Caution:

It's important to note that the error "SQLSTATE[HY000]: General error: 2031" can also occur if you bind multiple values to the same parameter name elsewhere in your code, even unrelated to LIMIT clauses. Therefore, always double-check your parameter binding to ensure that each name is used only once.

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