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Status: published
Programming, Software and application
2020-12-07 03:13:23
Oracle Dual Table
1809
Introduction to Oracle Database Oracle Tables and Data definition Modifying data Oracle Query and Filter Oracle data types Joining tables Oracle Operators Grouping data Constraints
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The DUAL table is a special one-row table present by default in all Oracle database installations. It is suitable for use in selecting a pseudocolumn such as SYSDATE or USER. The table has a single VARCHAR2(1) column called DUMMY that has a value of 'X'.
There may be a situation where we want to query something that is not from a table. For example, getting the current date or querying a simple arithmetic expression like 2+2.
In Oracle, clause FROM is not exceptional. If we don’t write the FROM clause in Oracle, we’ll get an error.
To print out the result of the calculation
Select 2*4 from dual
To print the server current date.
Select sysdate from dual