Question

在SQL语句的声明中，我根据用户的输入实现了if / else语句。这句话：

    if($form['filter']['date'] && $form['filter']['dateTill'] == ""){
        $sql .= '(select results.completed from results where results.client_id = c.id and results.completed IS NOT NULL AND results.completed > "'.$form['filter']['date'].'" order by results.id desc limit 1) AS last_completed_analysis, ';
    } else if($form['filter']['dateTill'] && $form['filter']['dateTill'] == "") {
       $sql .= '(select results.completed from results where results.client_id = c.id and results.completed IS NOT NULL AND results.completed < "'.$form['filter']['dateTill'].'" order by results.id desc limit 1) AS last_completed_analysis, ';
    } else if($form['filter']['dateTill'] && $form['filter']['dateTill']){
        $sql .= '(select results.completed from results where results.client_id = c.id and results.completed IS NOT NULL AND results.completed > "'.$form['filter']['date'].'" AND results.completed <"'.$form['filter']['dateTill'].'" order by results.id desc limit 1) AS last_completed_analysis, ';
    }
    else {
        $sql .= '(select results.completed from results where results.client_id = c.id and results.completed IS NOT NULL order by results.id desc limit 1) AS last_completed_analysis, ';
    }

所有这些都是last_completed_analysis别名。但是，is not null不起作用，因此我想声明一个带有is not null statement的where子句，如：

WHERE last_completed_analysis IS NOT NULL

然而..这不起作用。我可以复制粘贴last_completed_analysis的整个声明，但这段代码对我来说太长了，我知道它可以做得更好......有人可以帮我宣布这个where子句吗？

Answer 1

您不能在where condition

中使用别名

您可以按顺序使用别名，也可以在分组中的最新版本中使用，但不能在..

中使用

这是因为以特定顺序评估了列区域，并且在评估where条件时，别名（目前）尚未解析

所以你应该使用完整的代码，例如：

  WHERE (select results.completed 
          from results 
          where results.client_id = c.id 
          and results.completed  
          IS NOT NULL order by results.id desc limit 1) IS NOT NULL

并小心使用基于字符串连接的非用户输入..

在where子句SQL中使用别名

1 个答案: