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...
truly, why no. Why not a date you would ask then. The column, its name, its datatype and even its value are NOT relevant. DUAL exists solely as a means to have a 1 row table we can reliably select from. Thats all. 3.Does it contain one row by default. yes, when we build the...
In Oracle, theSELECTstatement must have aFROMclause. However, some queries don’t require any table for example: SELECTUPPER('This is a string')FROMwhat_table;Code language:SQL (Structured Query Language)(sql) In this case, you might think about creating a table and use it in theFROMclaus...
According toWikipedia, the DUAL table was created by Oracle staff member Chuck Weiss. It was originally used to join internal views: I created the DUAL table as an underlying object in the Oracle Data Dictionary. It was never meant to be seen itself, but instead used inside a view that wa...
根据维基百科,DUAL表是由Oracle工作人员Chuck Weiss创建的。它最初用于连接内部视图: 我在Oracle数据字典中创建了DUAL表作为底层对象。它本来就不应该被自己看到,而是在一个需要查询的视图中使用。其想法是,您可以对DUAL表执行JOIN,并在结果中为表中的每一行创建两行。然后,通过使用GROUP by,可以对生成的连接进行汇总...
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: VARCHAR2
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...
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 ...
在oracle数据库中,dual表作为一个虚表存在的,因为oracle的查询操作语句必须满足格式:select columnname from tablename,其中的from所指向的表示必须的,所以某些非查询操作可以通过dual表来实现,如: --查看当前日期: Select sysdate from dual ; aaarticlea/png;base64,iVBORw0KGgoAAAANSUhEUgAAAL4AAABkCAIAAAC3sx2D...
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...