如何在此sql查询中使用0-20之间的范围？

Question

How I can use a range between 0-20 on this sql query?

  $sql = 'SELECT * FROM t1
          LEFT JOIN t2 ON t2.wid = t1.wid  
          UNION
          SELECT * FROM t1
          RIGHT JOIN t2 ON t2.wid = t1.wid
          limit 0, 20';
  $result = db_query($sql);//->fetchField();

Answer 1

Pass LIMIT into your query. and your limit would be variable every time like

$sql = 'SELECT * FROM (SELECT * FROM t1
          LEFT JOIN t2 ON t2.wid = t1.wid  
          UNION
          SELECT * FROM t1
          RIGHT JOIN t2 ON t2.wid = t1.wid) AS A LIMIT'.$start.','.$end

Answer 2

please please sanatize your query as this is very easy to SQL inject. For drupal it should be:

$result = db_query('SELECT * FROM (SELECT * FROM t1
      LEFT JOIN t2 ON t2.wid = t1.wid  
      UNION
      SELECT * FROM t1
      RIGHT JOIN t2 ON t2.wid = t1.wid) AS A LIMIT :min, :max',
      array('min' => $min, 'max' => $max));

There are better Drupal ways to write this but this is ok as long as you pass the variables as arguments.