增加了Driver对表中某字段通过主键批量更新的功能.

测试用代码.
    	$m=M('think\model\Adv:log');
    	for($i=0;$i<=10000;$i++)
    	{
    		$m->bulkSave(array('id'=>$i,'admin_id'=>$i*2));
    	}
    	$m->bulkSave(true);
对一万条记录的特定字段做单独更新,耗时0.46秒.如不使用字段绑定或者缩减绑定字符.可能会更小.

library/think/db/Driver.php

@@ -924,6 +924,51 @@ abstract class Driver
         return $this->execute($sql, $this->getBindParams(true), !empty($options['fetch_sql']) ? true : false);
     }
 
+    /**
+     * 批量更新某字段
+     * @access public
+     * @param mixed $field 字段名
+     * @param mixed $pk 主键名 
+     * @param mixed $dataSet 数据集 
+     * @param mixed $operator 运算符
+     * @param array $options 参数表达式
+     **/
+    public function updateFieldAll($field,$pk,$dataSet,$operator = '=',$options = [])
+    {
+        $values      = [];
+        $this->bind = array_merge($this->bind, !empty($options['bind']) ? $options['bind'] : []);
+        $field = $this->parseKey($field);
+        $pk = $this->parseKey($pk);
+        if(in_array($operator,['+','-'])){
+            $operator = '= ' . $field . $operator;
+        }
+        
+        $value = '';
+        foreach ($dataSet as $key => $val) {
+            if (is_array($val) && 'exp' == $val[0]) {
+                $value = $val[1];
+            } elseif (is_null($val)) {
+                $value = 'NULL';
+            } elseif (is_scalar($val)) {
+                if (0 === strpos($val, ':') && isset($this->bind[substr($val, 1)])) {
+                    $value = $val;
+                } else {
+                    $name    = count($this->bind);
+                    $value = ':' .  $_SERVER['REQUEST_TIME'] . '_' . $name;
+                    $this->bindParam( $_SERVER['REQUEST_TIME'] . '_' . $name, $val);
+                }
+            }
+            //没使用过非数字主键,怎么处理比较合适?
+            $values[] = " WHEN " .$key." THEN " . $value;
+         }
+         
+        $sql = 'UPDATE ' . $this->parseTable($options['table']) . ' SET ' . $field . $operator . ' CASE ' . $pk . implode(' ', $values) . ' END ' ;
+        //查询条件需和WHEN THEN对一致
+        $sql .= ' WHERE ' . $pk . ' in (' . implode(',',array_map([$this,'parseValue'],array_keys($dataSet))) . ')';
+        $sql .= $this->parseComment(!empty($options['comment']) ? $options['comment'] : '');
+        return $this->execute($sql, $this->getBindParams(true), !empty($options['fetch_sql']) ? true : false);
+    }
+    
     /**
      * 批量插入记录
      * @access public