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Meta-SQL: Towards practical meta-querying

Meta-SQL: Towards practical meta-querying. Gottfried Vossen University of Muenster. Jan Van den Bussche Stijn Vansummeren Limburgs Universitair Centrum. Context. Enterprise databases contain not only data but also queries: view definitions stored procedures usage logs workloads

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Meta-SQL: Towards practical meta-querying

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  1. Meta-SQL: Towards practical meta-querying Gottfried Vossen University of Muenster Jan Van den Bussche Stijn Vansummeren Limburgs Universitair Centrum

  2. Context Enterprise databases contain not only data but also queries: • view definitions • stored procedures • usage logs • workloads • software engineering Stored as long strings… • Difficult to query in standard SQL

  3. Goal Allow meta-querying: query the stored queries together with ordinary data • Which queries do the most joins? • Which queries return an empty answer? • What are common subexpressions in this workload? • If I do these updates, which materialized views change their value?

  4. Contribution Meta-SQL: conservative extension of SQL to allow meta-querying • store queries in XML • call XSLT within SQL • add XML-variables • add an EVAL function Works on top of any SQL99-compliant DBMS Prototype with DB2 UDB

  5. Call XSLT within SQL Which queries do the most joins? select name from Views where count_tables(def) = (select max( ( )) from Views) count_tables def written in XSLT view definition in XML

  6. XML-variables What are the common subqueries? arbitrary Xpath-expression select s from Views, s in def[ ] group by s having count(name)>=2 //query s ranges over all query-subelements of stored query

  7. EVAL function Which queries return an empty answer? select name from Views where not exists (select * from EVAL(def)) EVAL produces query results in SQL row variable UEVAL produces them in XML-variable

  8. Implementation compilation execution XSLT functions Meta-SQL query SQL statements (CREATE FUNCTION) Java wrappers Rewriting in SQL99 SAXON (XML processing) Extract (XML variables) EVAL

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