Question

在Oracle 11g上，我正在尝试创建一个包含FAST REFRESH ON COMMIT子句的HAVING的实体化视图。

快速刷新的一般限制

物化视图的定义查询限制如下：


它不能包含带子查询的HAVING子句。

但是如果我将HAVING count(*)>1（注意：没有子查询）添加到其他工作的物化视图中，我会收到此错误：

ORA-12054：无法为物化视图设置ON COMMIT刷新属性

dbms_mview.explain_mview()说：

REFRESH_FAST                   N
REFRESH_FAST_AFTER_INSERT      N   2011 a HAVING clause is present

实际命令：

SQL>  create materialized view mv1 refresh fast on commit as
  2      select UserId, count(*) from USERS group by UserId;

Materialized view created.

SQL> DROP MATERIALIZED VIEW mv1;

Materialized view dropped.

SQL> create materialized view mv1 refresh fast on commit as
  2      select UserId, count(*) from USERS group by UserId
  3          having count(*)>1; -- the only difference
    having count(*)>1
                    *
ERROR at line 5:
ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized view

注意：已创建物化视图日志（否则即使第一个示例也不起作用）。

为什么不起作用？有没有人知道带有HAVING子句的MV示例？所以至少我可以从那里开始（我用谷歌搜索但没有找到）。

注意2：我想要HAVING的原因是将视图中的行数从数千甚至数百万减少到几个。节省存储空间（并可能获得性能）。

PS：使用的精确Oracle数据库版本：11.2.0.3.0

Answer 1

是的，文档似乎不准确。

作为一种解决方法，您可以尝试实现嵌套的物化视图。

class UserProfile: UITableViewController {


    override func viewDidLoad() {
        super.viewDidLoad()          

        // Uncomment the following line to preserve selection between presentations
        // self.clearsSelectionOnViewWillAppear = false

        // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
        // self.navigationItem.rightBarButtonItem = self.editButtonItem()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    // MARK: - Table view data source

  override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        // #warning Incomplete implementation, return the number of sections
        return 1
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        // #warning Incomplete implementation, return the number of rows
        return 2
    }

    /*
    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("reuseIdentifier", forIndexPath: indexPath)

        // Configure the cell...

        return cell
    }
    */

    /*
    // Override to support conditional editing of the table view.
    override func tableView(tableView: UITableView, canEditRowAtIndexPath indexPath: NSIndexPath) -> Bool {
        // Return false if you do not want the specified item to be editable.
        return true
    }
    */


    // Override to support editing the table view.
 /**   override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
        if editingStyle == .Delete {
            // Delete the row from the data source
            tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
        } else if editingStyle == .Insert {
            // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
        }    
    } **/

    /*
    // Override to support rearranging the table view.
    override func tableView(tableView: UITableView, moveRowAtIndexPath fromIndexPath: NSIndexPath, toIndexPath: NSIndexPath) {

    }
    */

    /*
    // Override to support conditional rearranging of the table view.
    override func tableView(tableView: UITableView, canMoveRowAtIndexPath indexPath: NSIndexPath) -> Bool {
        // Return false if you do not want the item to be re-orderable.
        return true
    }
    */

    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        // Get the new view controller using segue.destinationViewController.
        // Pass the selected object to the new view controller.
    }
    */

}

物化视图使用HAVING子句快速刷新？

1 个答案: