Altova's XML Spy has a feature that will generate SQL DDL Script from an XSD file. XML Spy will cost you some money though.
Interestingly enough, a developer used a really clever trick of using an XSLT translation to create the DDL script from an XSD file. They have outlined it in two parts here and here.
I might have to try this out myself for future use...
EDIT: Just found this question asked previously here...
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