Method and apparatus for associating logical conditions with the re-use of a database query execution strategy

A computer program product for database query optimization comprising:

• a plurality of computer executable instructions recorded on signal-bearing media, wherein said instructions, when executed by at least one computer system, cause the at least one computer system to perform the steps of:
• generating a query execution strategy for a database query, said database query containing at least one condition comparing a first database field to an imported variable value;
• generating a query execution strategy condition expression associated with said query execution strategy, said query execution strategy condition expression expressing at least one condition on the use of said query execution strategy, said at least one condition of said query execution strategy condition expression referencing said imported variable value, said at least one condition of said query execution strategy condition expression being generated by:
• (a) negating a predicate referencing said first database field contained in a logical expression defining an applicability of said query execution strategy,
• (b) inserting said negated predicate into said at least one condition of said query comparing a first database field to an imported variable value, and
• (c) performing a transitive closure of the expression resulting from said inserting step;
• receiving an invocation of said database query including a first instance of said imported variable value;
• evaluating said query execution strategy condition expression using said first instance of said imported variable value;
• and
• using said query execution strategy to execute said database query including said first instance of said imported variable value depending on the results of said evaluating step.

A computer system, comprising:

• at least one processor;
• a data storage for storing a database;
• a database management facility embodied as a plurality of instructions executable on said at least one processor, said database management facility including a query engine which executes logical queries against said database and a query optimizer for generating execution strategies for executing logical queries against said database;
• wherein a first execution strategy generated by said query optimizer for a first logical query contains at least one condition comparing a first database field of said database to an imported variable value, said first execution strategy employing a database subset data structure containing data from a subset of records in said database, said subset having a scope defined with reference to said first database field;
• wherein said database management facility automatically generates a query execution strategy condition expression associated with said first execution strategy, said query execution strategy condition expression expressing at least one condition on the use of said first execution strategy, said at least one condition limiting said imported variable value to a range of values in which said at least one condition of said query is within the scope of said database subset data structure;
• and
• wherein, responsive to invoking said first database query including a first instance of said imported variable value, said database management facility evaluates said query execution strategy condition expression using said first instance of said imported variable value;
• and uses said first execution strategy to execute said first database query including said first instance of said imported variable value depending on the results of the evaluation.