Is Using Oracle's DUAL Table the Best Way to Perform SELECT Queries Without a FROM Clause?

Performing SELECT Queries without a FROM Clause in Oracle

In contrast to SQL Server, Oracle requires a FROM clause in SELECT statements. Therefore, using the dual table to facilitate these queries in Oracle has been a common practice.

Is Using the Dual Table a Suitable Approach?

Yes, utilizing the dual table for such queries is generally considered good practice. Dual is an in-memory table, providing fast execution by avoiding I/O operations.

Historically, dual featured two records, allowing it to serve as a duplicate recordset in join operations. Currently, it consists of a single record, but the following query demonstrates how to generate multiple rows from it:

SELECT  level
FROM    dual
CONNECT BY
        level <= 100

Additional Notes

MySQL also supports the dual table and the fromless syntax seen in SQL Server. It's important to remember that the absence of a FROM clause is not supported in Oracle without the use of the dual table workaround.

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