To get pager on page

Use of pager query :

 Drupal 4.6 - 6 :

 pager_query($query, $limit = 10, $element = 0, $count_query = NULL)

Perform a paged database query. Use this function when doing select queries you wish to be able to page. The pager uses LIMIT-based queries to fetch only the records required to render a certain page. However, it has to learn the total number of records returned by the query to compute the number of pages (the number of records / records per page).

This is done by inserting "COUNT(*)" in the original query. For example, the query "SELECT nid, type FROM node WHERE status = '1' ORDER BY sticky DESC, created DESC" would be rewritten to read "SELECT COUNT(*) FROM node WHERE status = '1' ORDER BY sticky DESC, created DESC". Rewriting the query is accomplished using a regular expression.

 $output1 .= theme('pager',null, $count, 0);
This is used to get the number.
We can use this pager query in "Custom Search" to show the o/p with pagination.
Use pager_query instead of db_query to get pager on the result page.

NOTE : Do not use Group BY clause in the $count_query in pager query.
For more details Click Here

For Example :

function taxonomy_select_nodes($tids = array(), $operator = 'or', $depth = 0, $pager = TRUE, $order = 'n.sticky DESC, n.created DESC') {
  if (count($tids) > 0) {
    // For each term ID, generate an array of descendant term IDs to the right depth.
    $descendant_tids = array();
    if ($depth === 'all') {
      $depth = NULL;
    }
    foreach ($tids as $index => $tid) {
      $term = taxonomy_get_term($tid);
      $tree = taxonomy_get_tree($term->vid, $tid, -1, $depth);
      $descendant_tids[] = array_merge(array($tid), array_map('_taxonomy_get_tid_from_term', $tree));
    }

    if ($operator == 'or') {
      $str_tids = implode(',', call_user_func_array('array_merge', $descendant_tids));
      $sql = 'SELECT DISTINCT(n.nid), n.sticky, n.title, n.created FROM {node} n INNER JOIN {term_node} tn ON n.nid = tn.nid WHERE tn.tid IN ('. $str_tids .') AND n.status = 1 ORDER BY '. $order;
      $sql_count = 'SELECT COUNT(DISTINCT(n.nid)) FROM {node} n INNER JOIN {term_node} tn ON n.nid = tn.nid WHERE tn.tid IN ('. $str_tids .') AND n.status = 1';
    }
    else {
      $joins = '';
      $wheres = '';
      foreach ($descendant_tids as $index => $tids) {
        $joins .= ' INNER JOIN {term_node} tn'. $index .' ON n.nid = tn'. $index .'.nid';
        $wheres .= ' AND tn'. $index .'.tid IN ('. implode(',', $tids) .')';
      }
      $sql = 'SELECT DISTINCT(n.nid), n.sticky, n.title, n.created FROM {node} n '. $joins .' WHERE n.status = 1 '. $wheres .' ORDER BY '. $order;
      $sql_count = 'SELECT COUNT(DISTINCT(n.nid)) FROM {node} n '. $joins .' WHERE n.status = 1 '. $wheres;
    }
    $sql = db_rewrite_sql($sql);
    $sql_count = db_rewrite_sql($sql_count);
    if ($pager) {
      $result = pager_query($sql, variable_get('default_nodes_main', 10), 0, $sql_count);
    }
    else {
      $result = db_query_range($sql, 0, variable_get('feed_default_items', 10));
    }
  }

  return $result;
}

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