Older PDO placeholder parsing could treat a quote preceded by a backslash as still open, even when PostgreSQL with standard_conforming_strings treated that quote as the end of the literal. Later placeholders then appeared to be missing. The safest query avoids embedding the backslash at all.
Last updated: November 10, 2026.
<?php
$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$stmt = $pdo->prepare(
'SELECT :first AS first_value, :slash AS slash_value,
:second AS second_value'
);
$stmt->execute([
'first' => 'alpha',
'slash' => '\\',
'second' => 'beta',
]);
$row = $stmt->fetch(PDO::FETCH_ASSOC);Placeholders represent complete values, so binding the backslash removes the SQL-literal ambiguity and keeps user data outside the query text. Do not concatenate a quoted value merely to make the placeholder count match.
Know which parser sees the query
The PDO::prepare documentation explains that PDO may emulate prepares or rewrite placeholder styles. Before PHP 8.4, its parser recognized nonstandard backslash escapes around quotes, which could misidentify later markers. PHP 8.4 introduced driver-specific SQL parsers, and the PDO PostgreSQL documentation confirms that this driver has a PostgreSQL-aware parser.
Record the PHP version, pdo_pgsql version, emulation setting, exact SQL, and SQLSTATE. A generic “Invalid parameter number” does not prove that the supplied array is wrong; first compare the markers PDO actually detected.
Write unambiguous PostgreSQL literals
PostgreSQL’s lexical syntax reference says ordinary string constants do not interpret backslash escapes when standard_conforming_strings is on, the default since PostgreSQL 9.1. When an SQL constant genuinely needs escapes, use an explicit E'...' string and test it independently.
Prefer upgrading to a supported PHP release over depending on historical parser behavior. Keep emulation disabled unless a documented compatibility requirement demands it, bind each value once, and add a regression test containing a trailing backslash plus a later placeholder. That test should run against the same PostgreSQL and PHP versions used in production.
