System and method of query transformation

1 . A query transformation system for transforming nested aggregates in a query, the query transformation system comprising:

a nested aggregate analysis module for analysing a query that is not supported by a target database system; and

a nested aggregate transformation module for transforming the query into a semantically equivalent query that is supported by the target database system.

2 . The query transformation system as claimed in claim 1 , wherein the nested aggregate analysis module includes:

a nested aggregate detection unit for traversing a query and detecting a nested aggregate in the query; and

a nested aggregate tagging unit for traversing a query and tagging the nested aggregate.

3 . The query transformation system as claimed in claim 1 , wherein the nested aggregate transformation module includes:

a derived table for storing a copy of a tagged nested aggregate; and

a query editor for inserting the tagged nested aggregate into a query that is supported by a target database system.

4 . A method of nested aggregate transformation, the method comprising the steps of:

analysing a query that is not supported by a target database system; and

transforming the query into a semantically equivalent query that is supported by the target database system.

5 . The method as claimed in claim 4 , wherein the step of analysing includes the steps of:

detecting a nested aggregate in a select list of a query; and

adding a tag to the nested aggregate.

6 . The method as claimed in claim 4 , wherein the step of analysing includes the steps of:

creating a derived table;

adding a column reference to a select list in the derived table; and

adding the tagged nested aggregate to the select list of the derived table.

7 . A method of nested aggregate transformation, the method comprising the steps of:

generating a derived table to compute aggregates;

extracting nested aggregates and moving nested aggregates into a select list of the derived table; and

determining whether the transformation is to be performed, including the steps of:

detecting nested aggregates; and

detecting framed aggregates and report aggregates;

if nested aggregates are detected, performing the transformation, including the steps of:

marking a nested aggregate for insertion into an inner select list;

marking a report aggregate for insertion into the inner select list if it does not contain a nested aggregate or there are framed aggregates present; and

detecting framed aggregates; and

adding expressions to the inner select list of the derived table.

8 . A computer data signal embodied in a carrier wave and representing sequences of instructions which, when executed by a processor, cause the processor to perform a method of nested aggregate transformation, the method comprising the steps of:

analysing a query that is not supported by a target database system; and

transforming the query into a semantically equivalent query that is supported by the target database system.

9 . A computer-readable medium having computer readable code embodied therein for use in the execution in a computer of a method of nested aggregate transformation, the method comprising the steps of:

analysing a query that is not supported by a target database system; and

transforming the query into a semantically equivalent query that is supported by the target database system.

10 . A computer program product for use in the execution in a computer of a query transformation system for transforming nested aggregates in a query, the computer program product comprising:

a nested aggregate analysis module for analysing a query that is not supported by a target database system; and

a nested aggregate transformation module for transforming the query into a semantically equivalent query that is supported by the target database system.