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...
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...
dual是一个表,有一个名为DUMMY,类型为VARCHAR2(1)。DUMMY这个词在英文中的含义为“something designed to resemble and serve as a substitute for the real...
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...
1.dual 确实是一张表.是一张只有一个字段,一行记录的表. 2.习惯上,我们称之为'伪表'.因为他不...
The table named DUAL is a small table in the data dictionary that Oracle and user-written programs can reference to guarantee a known result. This table has one column called DUMMY and one row containing the value X. 这个名称为dual的表是位了保证oracle和用户程序能够引用一个已知的值。这个表只...
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 ...
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...
Oracle Database/ Release 19 SQL言語リファレンス DUALは、データ・ディクショナリとともにOracle Databaseによって自動的に作成された表です。DUALは、ユーザーSYSのスキーマにありますが、すべてのユーザーがDUALという名前でアクセスすることができます。VARCHAR2(1)として定義されているDU...
-- DUAL is a table in Oracle database that is typically used to perform calculations or as a placeholder FROM DUAL; Explanation: This SQL code selects all columns from the DUAL pseudo-table. The DUAL table is a special one-row, one-column table in Oracle database. ...