Why Does Oracle Require a FROM Clause in SELECT Statements, and What Are the Best Workarounds?

Oracle's Restriction on SELECT without a FROM Clause

While SQL Server permits SELECT statements without referencing a table, Oracle mandates the inclusion of a FROM clause. This poses a question for users accustomed to utilizing such queries.

To circumvent this limitation, Oracle developers often resort to the dual table. However, concerns arise regarding the effectiveness and best practices for this approach.

Use of the DUAL Table

Oracle's dual table is a single-record table that serves as a convenient placeholder for SELECT statements that do not require access to specific table data. Its usage, as illustrated below, has become a common practice:

Select 1,2+3, 'my dummy string' FROM DUAL

Advantages of DUAL Table Usage

Using the dual table offers several advantages:

1. Lightweight Access: Dual is an in-memory table, which eliminates the need for I/O operations when selecting the DUMMY column.
2. Flexibility: It allows for generating an arbitrary number of rows using CONNECT BY queries.
3. Prevalence: Dual table support is also available in MySQL, enhancing its cross-platform compatibility.

Alternatives to DUAL Table Usage

While the dual table remains a viable option, alternative approaches can also be considered:

1. Temporary Tables: Creating temporary tables specifically for such queries can avoid the overhead of using the dual table.
2. Inline Queries: Embedding the query within a subquery or CASE statement can eliminate the need for a FROM clause.

Conclusion

In Oracle, SELECT statements without a FROM clause are indeed prohibited. Using the dual table has emerged as a practical workaround, offering advantages such as lightweight access and flexibility. However, alternatives like temporary tables and inline queries may also be considered for specific scenarios. Ultimately, the choice depends on the requirements and preferences of the developer.

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