bindParam正在打破SQL查询

Question

I have a query which i am building like so:

$filmQuery = "
  SELECT nfc_film.title, nfc_film.film_id, nfc_film.description, nfc_film.release_year, nfc_film.rating, nfc_film.last_update, nfc_category.name FROM nfc_film
      JOIN nfc_film_category
        ON nfc_film.film_id = nfc_film_category.film_id
      JOIN nfc_category
        ON nfc_film_category.category_id = nfc_category.category_id";

  if($search_term && $category){
    $filmQuery .= "
    WHERE
      nfc_film.title LIKE :searchterm
    AND
      nfc_category.name = :category";

  } else if ($search_term && !$category) {
    $filmQuery .= "
    WHERE
      nfc_film.title LIKE :searchterm";
  } else if (!$search_term && $category) {
    $filmQuery .= "
    WHERE
      nfc_category.name = :category";
  }

  $filmQuery .= "
    LIMIT 10
    OFFSET 0
      ";

This seems to work correctly, i have checked the the variable and ran it in my DBMS and it works.

So then i bind the Params (includes param binds for another query):

  if($search_term != ''){
    $sqlGetFilms->bindParam(':searchterm', $sqlSearchTerm, PDO::PARAM_STR);
    $sqlCountFilms->bindParam(':searchterm', $sqlSearchTerm, PDO::PARAM_STR);
  }

  if($category != ''){
    $sqlGetFilms->bindParam(':category', $category, PDO::PARAM_STR);
    $sqlCountFilms->bindParam(':category', $category, PDO::PARAM_STR);
  }

  if($page != ''){
    $sqlGetFilms->bindParam(':page', $page, PDO::PARAM_INT);
  }

The result that i get when i execute this is nothing.

When i remove the bindParams and replace the parameters in the query with static values, the query returns results.

So, why are the bindParams breaking my query?

EDIT: These are the sql statements for 1. no $search_term or category 2. both $search_term and $category:

SELECT nfc_film.title, nfc_film.film_id, nfc_film.description, nfc_film.release_year, nfc_film.rating, nfc_film.last_update, nfc_category.name
    FROM nfc_film
  JOIN nfc_film_category
    ON nfc_film.film_id = nfc_film_category.film_id
  JOIN nfc_category
    ON nfc_film_category.category_id = nfc_category.category_id  LIMIT 10 OFFSET 0


SELECT nfc_film.title, nfc_film.film_id, nfc_film.description, nfc_film.release_year, nfc_film.rating, nfc_film.last_update, nfc_category.name
    FROM nfc_film
  JOIN nfc_film_category
    ON nfc_film.film_id = nfc_film_category.film_id
  JOIN nfc_category
    ON nfc_film_category.category_id = nfc_category.category_id 
    WHERE
      nfc_film.title LIKE :searchterm
    AND
      nfc_category.name = :category LIMIT 10 OFFSET 0