WordPress: Search in ACF fields, functions.php

wordpress_search_in_custom_fields.php

<?php
///////////////////////////////////
/// SUPPORT FOR SEARCHING IN ACF
///////////////////////////////////
/* Join posts and post-meta tables
*
 * http://codex.wordpress.org/Plugin_API/Filter_Reference/posts_join
 */
function cf_search_join( $join ) {
    global $wpdb;

    if ( is_search() ) {
        $join .=' LEFT JOIN '.$wpdb->postmeta. ' ON '. $wpdb->posts . '.ID = ' . $wpdb->postmeta . '.post_id ';
    }

    return $join;
}
add_filter('posts_join', 'cf_search_join' );

/**
 * Modify the search query with posts_where
 *
 * http://codex.wordpress.org/Plugin_API/Filter_Reference/posts_where
 */
function cf_search_where( $where ) {
    global $pagenow, $wpdb;

    if ( is_search() ) {
        $where = preg_replace(
            "/\(\s*".$wpdb->posts.".post_title\s+LIKE\s*(\'[^\']+\')\s*\)/",
            "(".$wpdb->posts.".post_title LIKE $1) OR (".$wpdb->postmeta.".meta_value LIKE $1)", $where );
    }

    return $where;
}
add_filter( 'posts_where', 'cf_search_where' );

/**
 * Prevent duplicates
 *
 * http://codex.wordpress.org/Plugin_API/Filter_Reference/posts_distinct
 */
function cf_search_distinct( $where ) {
    global $wpdb;

    if ( is_search() ) {
        return "DISTINCT";
    }

    return $where;
}
add_filter( 'posts_distinct', 'cf_search_distinct' );

When running a WP_Query for getting posts by custom fields name it is throwing this error

WordPress database error: [Not unique table/alias: 'wp_postmeta']

My Query

// args
$argschild = array(
	'numberposts'	=> 2,
	'post_type'		=> 'contactdirectory',
	'meta_key'		=> 'select_parent',
	'meta_value'	=> $parentid
);

// query
$the_query_child = new WP_Query( $argschild );