6) the optimizer understands dual is a magic, special 1 row table. It stopped on the select * because there is to be one row in there. Its just the way it works. Hopefully you reset dual back to 1 row after your testing or you just totally broke your database! 7) like I said, ...
things basedonthat.8) dual = magic. dualisa one row table however having morethen1orlessthenoneisdangerous. You are updating the data dictionary. You should naturally expect very bad thingstohappen. 简单总结,意思如下: DUAL is a convienence table The column, its name, its datatype and eve...
Licensing: PostgreSQL is distributed under the PostgreSQL License, a permissive open source license. In contrast, MySQL offers dual licensing options: the GNU General Public License (GPL) for open-source projects and a proprietary commercial license for other uses. Data types: PostgreSQL provides a ...
SQL profile is a collection of additional statistical information stored in the data dictionary that helps the optimizer to generate the best plan for the query. SQL profile is managed through SQL_TUNE package of SQL tuning advisor. i.e when we run SQL tuning advisor against a query, The tun...
Eg:- Select 1 from dual; returns 1 as there is only one record in dual. Select 1 from v$session; returns 7 1â s if there are 7 records on v$sessionHere is a table called TAB1 that has 3 rows.SQL> select * from tab1; ENO--- 101 102 103Now i...
Using Message Queuing COM Components in Visual C++ and C Opening Local Queues Visual Basic Code Example: Retrieving MSMQQueueInfo.Authenticate MSMQ Glossary: M IFileOpenDialog Notifications Notifications Toolbar Controls MSMQQueueInfo.IsWorldReadable2 Visual Basic Code Example: Sending a Message Using a...
FROM DUAL The output of the above query will be Institute The function is mostly utilized in adding characters to the string and deleting the characters from a large string. Let me explain this with a practical example. I am creating a table named Offers that contain the Offer list. The Of...
"explicit value must be specified for identity column in table" error in SQL 2000 "FROM clause have the same exposed names. Use correlation names to distinguish them" "No transaction is active." error when trying to send a transactional SQL statment over MSDTC "Restricted data type attribute ...
NSO 可以这样理解:nested subquery optimizing ,把in转换为JOIN,把NOT IN转换为 anti join(如果能确保列不为null) 那么什么时候oracle会生成 VW_NSO_1 这样的视图呢,请看下面的几个例子(基于ORACLE10g): SQL> select count(*) from t1 where object_id not in (select MAX(object_id) from t2 GROUP BY ...
百度试题 题目SQL> SELECT TRUNC(ROUND(156.00,-1),-1) FROM DUAL; What would be the outcome?(结果是什么?) A. 16 B. 100 C. 160 D. 200 E. 150 相关知识点: 试题来源: 解析 C.160 反馈 收藏