Cartesian Product Elimination  -

detect 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

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

Invalid Outer Join  

before

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

after

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

Transitivity  

Before

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

After

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  

Before

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

After

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

NULL Column  

Before

SELECT * FROM employee 
WHERE manager_id != NULL

After

SELECT * FROM employee 
WHERE manager_id IS NUL

Push Subquery  

Before

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

After

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 

Quick Fixes Demo File