Summary: Oracle INTERNALS: DUAL reads every Monday on week, I want to use the friends on the forum to organize Chinese, there is no one to do it, and white snow can only sort it. I hope that friends on the forum can actively participate, thank you. 1. Dual is built by SQL.BSQ. Each Database is built, and SQL.BSQ requires RUN once. So each Database will have Dual Table. 2. Who is DUAL Owner? - sys (select owner, table_name from dba_tables where table_name = 'dual'3. When is you often used? I use it most often, do Time Stamps.connect Internal; select to_char (sysdate,' YY) in Batch Script -Mon-dd hh: mi ') from dual; .............. As for the operation or see the Value of SEQUENCE, it is not much. Comparison of people who may be developed More. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ About the issue of Performance caused by DUAL. If you don't use a lot of DUAL, it seems to not consider I have not seen a database of ACCESS for thousands of Dual's database. But according to the article, establish index for DUAL (8i and previous), and often do the Analyzle Dual Comput Statistics. Or use where WHERE To create a view, you can make it exist in Memory. If you use it, you will reduce the Performance Cost. But I think these know it, wait for you to take time to study.
