于是以“X$DUAL oracle”为关键词google了一下,找到Tom的一篇文章 1.Whatisthe dual table, whatisits purpose. dualisjust a convienence table. You don't need to use it, you can use anything youwant. The advantagetodualisthe optimizer understands dualisa special one row, one column table --when...
Oracle Dual Table Summary: In this tutorial, you will learn about the OracleDUALtable, which is a special table used for evaluating expressions or calling functions. Introduction to the Oracle dual table# In Oracle, theSELECTstatement must have aFROMclause. However, some queries don’t require ...
oracle dual表 DUAL is a table automatically created by Oracle Database along with the data dictionary. DUAL is in the schema of the user SYS but is accessible by the name DUAL to all users. It has one column, DUMMY, defined to be VARCHAR2(1), and contains one row with a value X. ...
Oracle Database 10gリリース1以降では、DUMMY列を含まない式を計算する場合に、論理I/OがDUAL表で実行されません。この最適化は、実行計画でFAST DUALとしてリストされます。DUALのDUMMY列に対してSELECTを実行した場合、この最適化は行われず、論理I/Oが実行されます。 前...
首先,公司用的是Oracle数据库,关于Oracle数据库中的dual表,官方文档说明(The DUAL Table): DUALis a small table in the data dictionary that Oracle Database and user-written programs can reference to guarantee a known result. The dual table is useful when a value must be returned only once, for ...
dual本身就是一个单词,并非是某个词组的缩写.名词意为对数,形容词为双重的意思.在Oracle中dual指dual table,一个单行单列的虚拟表.1: DUAL table-- a special kind of one-row and one-column database table;2:dual is a table which is created by oracle along with the data dictionary. ...
我是一个拥有只读权限的用户)，我想查找10,000个唯一的id，我不能将它们放在IN()语句中，因为oracle...
In oracle it is possibile to use a statement like this select something from dual where dual is a special table on which you could select any field you like to It is a special purpose table that it is often used Any alternative in impala? At the moment what i need to do is a ...
SQL> create table dual2asselect*fromdual; Run Code Online (Sandbox Code Playgroud) 现在,您的查询有效: SQL>select4*5fromdual2;4*5---20 Run Code Online (Sandbox Code Playgroud) 早些时候,我说过双几乎像任何其他表一样工作。那么,什么时候它不像任何其他表一样工作? 如果没有选择...
dual table dual table has oneVARCHAR2column named dummy and contains a single row with the value X.DESCRIBEcommand shows the structure of the dual table: VARCHAR2SELECTFROM