Question

所以我正在研究一个现有系统，我正在试图找出他们如何设置mysql。他们有像这样的查询设置

    $this->db->select('nID, nAID');
    $this->db->where('bValid', 1);
    $this->db->where('nID', (int)$nID);
    $this->db->from('event');
    $this->db->group_by('nID, nAID');

    $query = $this->db->get();

此查询效果很好，但我需要设置子查询。我已经在SQL中编写了查询并对其进行了测试，以确认它是否有效，但我无法弄清楚如何翻译它。基本上我需要的不是从'事件'表中抓取，而是需要从我之前做出的子选择中获取。我怎么想象它会是。

    $this->db->select('nID, nAID');
    $this->db->where('bValid', 1);
    $this->db->where('nID', (int)$nID);
    $this->db->from(
         $this->db->select('something, somethingelse');
         $this->db->where('something', 1);
         $this->db->get();  
    );
    $this->db->group_by('nID, nAID');

    $query = $this->db->get();

Answer 1

            $this->db->select('nID, nAID');
            $this->db->where('bValid', 1);
            $this->db->where('nID', (int)$nID);
            $this->db->from('event');
            $this->db->group_by('nID, nAID');

转换为从事件中选择nID，nAID，其中bValid = 1，nId ='$ nID'group by nID

您的子查询

            $this->db->select('nID, nAID');
            $this->db->where('bValid', 1);
            $this->db->where('nID', (int)$nID);
            $this->db->from(
            $this->db->select('something, somethingelse');
            $this->db->where('something', 1);
            $this->db->get();  
            );
            $this->db->group_by('nID, nAID');

大致翻译为

            select nID, nAID select something,somethingelse where something=1 event where bValid=1 and nId='$nID' group by nID

我建议在循环中的每条记录上运行子查询

Answer 2

第1步：将此代码放入DB_active_rec.php

 // --------------------------------------------------------------------
    /**
    * Get SELECT query string
    *
    * Compiles a SELECT query string and returns the sql.
    *
    * @param    string    the table name to select from (optional)
    * @param    bool    TRUE: resets QB values; FALSE: leave QB vaules alone
    * @return    string
    */
   public function get_compiled_select($table = '', $reset = TRUE)
   {
       if ($table !== '')
       {
           $this->_track_aliases($table);
           $this->from($table);
       }

       $select = $this->_compile_select();

       if ($reset === TRUE)
       {
           $this->_reset_select();
       }

       return $select;
   }

第2步：试试这个

//Subquery
$this->db->select('something, somethingelse');
$this->db->where('something', 1);
$this->db->from('first_table');
$sub_query = $this->db->get_compiled_select();


$this->db->select('nID, nAID');
$this->db->where('bValid', 1);
$this->db->where('nID', (int)$nID);
$this->db->from("($sub_query) as tbl1");
$this->db->group_by('nID, nAID');

$query = $this->db->get();

告诉我它是否有效。

如何在PHP中创建子查询？

2 个答案: