The type cast behaviors of SQL and SPARQL are different. SQL will generally signal an error when an automatic cast fails. For example, a string can be compared to a date column if the string can be parsed as a date but otherwise the comparison should signal an error. In SPARQL, such situations are supposed to silently fail. Generally, SPARQL is much more relaxed with respect to data types.

These differences will be specially noticed if actual SQL data is processed with SPARQL via some sort of schema mapping translating references to triples into native tables and columns.

Also, even when dealing with the triple-oriented RDF_QUAD table, there are cases of joining between S and O such that the O can be a heterogeneous set of IRI's and other data whereas the S is always an IRI. The non-IRI to IRI comparison should not give cast errors but should silently fail. Also, in order to keep queries simple and easily optimizable, it should not be necessary to introduce extra predicates for testing if the O is n IRI before comparing with the S.

Due to these considerations, Virtuoso introduces a SQL statement option called QUIETCAST. When given in the OPTION clause of a SELECT, it switches to silent fail mode for automatic type casting.

The syntax is as follows:

SELECT ...
FROM .... OPTION (QUIETCAST)

This option is automatically added by the SPARQL to SQL translator. The scope is the enclosing procedure body.