$search_terms = "example search" // input post
// remove single quotes from search terms
$search_terms = str_replace("'","",$search_terms);

$sql = "SELECT
    post.ID,
    post.post_author,
    post.post_date,
    post.post_title,
    LEFT(post.post_content, 240) As post_content,
    post.post_name,
    post.post_type,
    post.comment_count,
    post.comment_status,
    MATCH (post_search.post_content,post_search.post_title) AGAINST (%s IN BOOLEAN MODE) AS score
FROM wp_posts post
LEFT JOIN wp_term_relationships term_rel
    ON post.ID = term_rel.object_id
LEFT JOIN wp_term_taxonomy term_tax
    ON term_rel.term_taxonomy_id = term_tax.term_taxonomy_id
LEFT JOIN wp_terms terms
    ON term_tax.term_id = terms.term_id
LEFT JOIN wp_posts_fulltext_search post_search
    ON post.ID=post_search.post_id
WHERE MATCH(post_search.post_content,post_search.post_title) AGAINST (%s IN BOOLEAN MODE) &&
    post.post_status = 'publish' &&
    post.post_type = 'post' &&
    (term_tax.description != '' &&
    term_tax.description NOT LIKE '%sample%')
GROUP BY post.ID
ORDER BY score DESC
LIMIT 0,20";

$results = $wpdb->get_results( $wpdb->prepare( $sql, $search_terms ) );

// remove single quotes from search terms
$search_terms = str_replace("'","",$search_terms);

$search_terms = mysql_real_escape_string($search_terms);

<?php
  $sql = $wpdb->prepare('query' [, value_parameter, value_parameter ... ] );
?>

$metakey = "Harriet's Adages";
$metavalue = "WordPress' database interface is like Sunday Morning: Easy.";

$wpdb->query( $wpdb->prepare( "
    INSERT INTO $wpdb->postmeta
    ( post_id, meta_key, meta_value )
    VALUES ( %d, %s, %s )",
        10, $metakey, $metavalue ) );

$metakey = "Harriet's Adages";
$metavalue = "WordPress' database interface is like Sunday Morning: Easy.";

$wpdb->query( $wpdb->prepare( "
    INSERT INTO $wpdb->postmeta
    ( post_id, meta_key, meta_value )
    VALUES ( %d, %s, %s )",
        array(10, $metakey, $metavalue) ) );

term_tax.description NOT LIKE '%sample%')

term_tax.description NOT LIKE '%%sample%%')