What considerations apply if I want to write portable SQL statements that work on many different databases? Is it enough to follow the SQL-92 standard?

Unfortunately, no. There are lots of databases and drivers out there with varying levels of support. It's worth taking note of all the getXXX and supportsXXX methods in the DatabaseMetaData class for those who want to provide and check everything.

However, a JDBC Compliant ( and that is a specific, meaningful term ) driver will always support ANSI SQL-92 Entry Level. For more information, see the SQL Conformance section in my JDBC 2.0 Fundamentals Short Course at the Java Developer Connection.