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Scalar subqueries for stored functions

Applies to ✅ Open Source Edition   ✅ Express Edition   ✅ Professional Edition   ✅ Enterprise Edition

This setting is useful mostly for the Oracle database, which implements a feature called scalar subquery caching, which is a good tool to avoid the expensive PL/SQL-to-SQL context switch when predicates make use of stored function calls.

With this setting in place, all stored function calls embedded in SQL statements will be wrapped in a scalar subquery:

SELECT 
  (SELECT my_package.format(LANGUAGE_ID) FROM dual)
FROM BOOK
DSL.using(configuration)
   .select(MyPackage.format(BOOK.LANGUAGE_ID))
   .from(BOOK)

If our table contains thousands of books, but only a dozen of LANGUAGE_ID values, then with scalar subquery caching, we can avoid most of the function calls and cache the result per LANGUAGE_ID.

Example configuration

Settings settings = new Settings()
    .withRenderScalarSubqueriesForStoredFunctions(true);

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