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3 SQL
The de facto language for database applications is SQL. It evolved through several phases of standardization to the version currently known as SQL-2003. The SQL standard provides an ideal language framework, in terms of standardization committee viewpoints. It is, however, hardly met by any of the existing (commercial) implementations. This is largely due to software legacy and backward compatibility requirements from their client base. See for instance the wikipedia on-line article on SQL standards.
In 2002 the first version of the SQL front end emerged. This late development made it possible to immediately start from the SQL'99 definition. As soon as the SQL'03 specifications became available, its content was taken as the primary frame of reference. The SQL development strategy is driven by immediate needs of the user base, so that less-frequently used features end up low on the development stack.
The architecture is based on a separate compiler module, which translates SQL statements into the MonetDB Assembly Language (MAL). In this process common optimization heuristics, specific to the relational algebra are performed. There are bindings for SQL with e.g. JDBC, PHP, and C, to integrate seamlessly in the existing developments environments.
The remainder of this chapter presents a synopsis of the language features. It provides a quick intro on the scope of the current implementation, mostly through examples. Proficiency in elementary use of SQL is assumed. If you are new to this world then pick up any of the introduction books and study it carefully, e.g. J. Melton and A.R. Simon, SQL:1999 Understanding Relational Language Components, ISBN 1558604561.