队列监控oracle脚本

Question

我正在尝试监视仪表板上的队列。 我希望我的选择即使队列表为空也能返回一些内容，看看我当前的 qry。

SELECT 'QueueName' Q_NAME,
       CASE 
       WHEN COUNT(*) = 0 
       THEN (SELECT 'Nothing to process Queue is empty' FROM DUAL)
       ELSE 'something in the Queue'
       END Q_STATUS,
       CASE
       WHEN MSG_STATE = 'READY' AND MIN(ENQ_TIME) > SYSDATE - 5/(24*60)
       THEN 'OK: processing'
       ELSE 'Nothing to process on Queue'
       END STATUS
FROM   QueueTable
GROUP BY MSG_STATE;

Answer 1

如果要在表为空时返回一行，则可以使用

UNION ALL

添加另一行（如果为空，则使用默认值），然后按优先级对行进行排序，队列的详细信息具有比默认值更高的优先级，并且仅输出最高优先级的行：

SELECT
FROM   (
  SELECT 'QueueName' AS Q_NAME,
         CASE 
         WHEN COUNT(*) = 0 
         THEN 'Nothing to process Queue is empty'
         ELSE 'something in the Queue'
         END AS Q_STATUS,
         CASE
         WHEN MSG_STATE = 'READY' AND MIN(ENQ_TIME) > SYSDATE - 5/(24*60)
         THEN 'OK: processing'
         ELSE 'Nothing to process on Queue'
         END AS STATUS,
         1 AS priority
  FROM   QueueTable
  GROUP BY MSG_STATE
UNION ALL
  SELECT 'QueueName',
         'Nothing to process Queue is empty',
         'Nothing to process on Queue',
         2
  FROM   DUAL
)
ORDER BY priority
FETCH FIRST ROW WITH TIES;