Performing SQL query optimization by simplifying sub-expressions

1. A method of processing a database query on a computer, the query including an expression, the method including:

the computer performing expression optimization on the expression;

the computer performing further query optimization to produce a result;

the computer saving the result in a machine memory;

the computer performing expression optimization before further query optimization; and

where the expression includes a sub-expression (“SE”), and where the expression optimization includes:

the computer representing the query as a tree structure;

the computer representing the expression in the tree structure as a parent node having a first child node and a second child node;

where the first child node represents the sub-expression;

where the second child node represents the portion of the expression that is not the sub-expression; and

where the parent node represents an operation between the first child node and the second child node;

the computer determining that the second child node represents the constant 0 and that the parent node represents an arithmetic operation selected from the group consisting of addition and subtraction; and

in response, the computer removing the parent node and its children from the tree structure and inserting the first child node in its place.

2. The method of claim 1 , where the query includes an assignment list clause and where one or more of the expressions are in the assignment list clause.

3. The method of claim 1 , where the query includes a WHERE clause, and where one or more of the expressions are in the WHERE clause.

4. The method of claim 1 , where further query optimization includes:

determining a satisfiability of the database query.

5. The method of claim 1 , where further query optimization includes:

determining a transitive closure of the database query.

6. The method of claim 1 , where further query optimization includes:

determining one or more plans for executing the query.

7. The method of claim 6 , where one of the one or more plans includes:

scanning a table to locate rows that satisfy one or more conditions; and

summing one or more columns in the rows that satisfy the one or more conditions.

8. The method of claim 1 , where further query optimization includes:

selecting an optimal plan from executing the database query.

9. The method of claim 1 , where further query optimization includes two or more optimizations selected from the group consisting of:

determining a satisfiability of the database query;

determining a transitive closure of the database query;

determining one or more plans for executing the query; and

selecting an optimal plan from executing the database query.

10. A computer program, stored on a tangible storage medium, for use in processing a database query, the query including an expression, the computer program including executable instructions that cause a computer to:

perform expression optimization on the expression;

perform further query optimization to produce a result;

save the result in a machine memory;

where the expression includes a sub-expression (“SE”), where expression optimization is performed before further query optimization, and where the computer program includes executable instructions that cause a computer to:

represent the query as a tree structure;

represent the expression in the tree structure as a parent node having a first child node and a second child node;

where the first child node represents the sub-expression;

where the second child node represents the portion of the expression that is not the sub-expression; and

where the parent node represents an operation between the first child node and the second child node;

determine that the second child node represents the constant 0 and that the parent node represents an arithmetic operation selected from the group consisting of addition and subtraction; and

in response, remove the parent node and its children from the tree structure and insert the first child node in its place.

11. The computer program of claim 10 , where the query includes an assignment list clause and where one or more of the expressions are in the assignment list clause.

12. The computer program of claim 10 , where the query includes a WHERE clause, and where one or more of the expressions are in the WHERE clause.

13. The computer program of claim 10 , where further query optimization includes:

determining a satisfiability of the database query.

14. The computer program of claim 10 , where further query optimization includes:

determining a transitive closure of the database query.

15. The computer program of claim 10 , where further query optimization includes:

determining one or more plans for executing the query.

16. The computer program of claim 15 , where one of the one or more plans includes:

scanning a table to locate rows that satisfy one or more conditions; and

summing one or more columns in the rows that satisfy the one or more conditions.

17. The computer program of claim 10 , where further query optimization includes:

selecting an optimal plan from executing the database query.

18. The computer program of claim 10 , where further query optimization includes two or more optimizations selected from the group consisting of:

determining a satisfiability of the database query;

determining a transitive closure of the database query;

determining one or more plans for executing the query; and

selecting an optimal plan from executing the database query.

19. A database system including:

a massively parallel processing system including:

one or more nodes;

a plurality of CPUs, each of the one or more nodes providing access to one or more CPUs;

a plurality of data storage facilities each of the one or more CPUs providing access to one or more data storage facilities;

a computer program for execution on the massively parallel processing system for processing a database query, the query including an expression, the computer program including executable instructions that cause one or more of the CPUs to:

perform expression optimization on the expression;

perform further query optimization to produce a result;

save the result in a memory;

where the expression optimization is performed before the further query optimization; and

where the expression includes a sub-expression (“SE”), and where expression optimization includes:

representing the query as a tree structure;

representing the expression in the tree structure as a parent node having a first child node and a second child node;

where the first child node represents the sub-expression;

where the second child node represents the portion of the expression that is not the sub-expression; and

where the parent node represents an operation between the first child node and the second child node;

determining that the second child node represents the constant 0 and that the parent node represents an arithmetic operation selected from the group consisting of addition and subtraction; and

in response, removing the parent node and its children from the tree structure and inserting the first child node in its place.

20. The database system of claim 19 , where the query includes an assignment list clause and where one or more of the expressions are in the assignment list clause.

21. The database system of claim 19 , where the query includes a WHERE clause, and where one or more of the expressions are in the WHERE clause.

22. The database system of claim 19 , where further query optimization includes:

determining a satisfiability of the database query.

23. The database system of claim 19 , where further query optimization includes:

determining a transitive closure of the database query.

24. The database system of claim 19 , where further query optimization includes:

determining one or more plans for executing the query.

25. The database system of claim 24 , where one of the one or more plans includes:

scanning a table to locate rows that satisfy one or more conditions; and

summing one or more columns in the rows that satisfy the one or more conditions.

26. The database system of claim 19 , where further query optimization includes:

selecting an optimal plan from executing the database query.

27. The database system of claim 19 , where further query optimization includes two or more optimizations selected from the group consisting of:

determining a satisfiability of the database query;

determining a transitive closure of the database query;

determining one or more plans for executing the query; and

selecting an optimal plan from executing the database query.