Magento后台Grid表使用了Group By导致统计出错的解决办法

Wrong Count in Admin Grid When Using Group By : Magento

If you have noticed or not, in edition 1.5 of Magento when you use GROUP BY clause in any Grid.php file in admin, the count always display wrong. Many times it displays 1 even if there are hundreds of records. Due to this your pagination also doesn’t work. This is a bug in Magento. Your getSize() always returns wrong count whereas total records in grid are proper.
To fix this, you need to edit one of your core file. As it’s not a good practice to edit core file, we will here override the core file.
Overriding LIB module
Copy Db.php file from
MAGENTO_FOLDER / lib / Varien / Data / Collection / Db.php

Paste it to your local directory so the resultant folder structure would look like this:
MAGENTO_FOLDER  / app / code / local / Varien / Data / Collection / Db.php

Now open this file to edit and replace getSelectCountSql function with below one

public function getSelectCountSql()      {          $this->_renderFilters();          $countSelect = clone $this->getSelect();          $countSelect->reset(Zend_Db_Select::ORDER);          $countSelect->reset(Zend_Db_Select::LIMIT_COUNT);          $countSelect->reset(Zend_Db_Select::LIMIT_OFFSET);          $countSelect->reset(Zend_Db_Select::COLUMNS);          if(count($this->getSelect()->getPart(Zend_Db_Select::GROUP)) > 0) {              $countSelect->reset(Zend_Db_Select::GROUP);              $countSelect->distinct(true);              $group = $this->getSelect()->getPart(Zend_Db_Select::GROUP);              $countSelect->columns("COUNT(DISTINCT ".implode(", ", $group).")");          } else {              $countSelect->columns('COUNT(*)');          }          return $countSelect;    }

Google了一下，解决的办法可以是重写MAGENTO_FOLDER / lib / Varien / Data / Collection / Db.php里面的getSelectCountSql()方法，拷贝原文件到本地代码池MAGENTO_FOLDER  / app / code / local / Varien / Data / Collection / Db.php，并进行修改。

如果不想重写Varien Db.php代码，还可以这么改：

可以在你Grid表所用的collection里面增加这个getSelectCountSql()方法，代码同上，覆盖该方法。