Cartesian product elimination

Detects Cartesian Joins and propose corrections based on analysis of statement, for example suggesting dept.deptno = emp.deptno if emp and dept had no join criteria.

Expression transformation

Identifies actions on predicates that might suppress index usage such as "where empid + 1 = 1 ", should be "where empid=0"

Invalid outer join

Identifies invalid outer joins and suggests more efficient alternatives.

BeforeAfter
SELECT * FROM employee e, customer c
WHERE e.employee_id = c.salesperson_id ( + )
AND c.state = 'CA'		SELECT * FROM employee e, customer c
WHERE e.employee_id = c.salesperson_id ( + )
AND c.state( + ) = 'CA' 

Transitivity

BeforeAfter
SELECT * FROM item i, product p, price pr
WHERE i.product_id = p.product_id
AND p.product_id = pr.product_id

SELECT * FROM item i, product p, price pr
WHERE i.product_id = p.product_id
AND p.product_id = pr.product_id
AND i.product_id = pr.product_id 

Move expression to WHERE clause 

BeforeAfter
SELECT col_a, SUM(col_b) FROM table_a
GROUP BY col_a HAVING col_a > 100		SELECT col_a, SUM(col_b) FROM table_a
WHERE col_a > 100 GROUP BY col_a 

NULL column 

BeforeAfter
SELECT * FROM employee
WHERE manager_id != NULL

SELECT * FROM employee
WHERE manager_id IS NULL 

Push subquery 

BeforeAfter
SELECT * FROM employee
WHERE employee_id = (SELECT MAX(salary) FROM employee)

SELECT employee.* FROM employee, (SELECT DISTINCT MAX(salary) col1 FROM employee) t1
WHERE employee_id = t1.col1 

Mismatched column types

Identify joins type mismatch such as number = character which might suppress use of Index.


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