0
It has six specific rule to be precise.....
1)Use impotence of selection and projection to generate appropriate selections and projections for each operand relation.
2)Push selections and projections down in the tree as far as possible.
3)push selections down to the leaves of the tree, and then apply them using the algebra of qualified relations; substitute the selection result with the empty relation if the qualification of the result is contradictory.
4)Use the algebra of qualified relations to evaluate the qualification of operands of joins; substitute the subtree, including the join and its operands, with the empty relation if the qualification of the result of join is contradictory.
5)In order to distribute joins which appear in the global query, unions must be pushed up,beyond the joins that we want to distribute.
6)In order to distribute grouping and aggregate function evaluations appearing in a global query,unions must be pushed up,beyond the corresponding group-by operation.
refer some books of distributed database design or contact me for further explanations...
Avik Chatterjee
Lecturer
Techno India Hooghly
9038223317
cavik81@gmail.com
What else can I help you with?
Make a word with these letters bbdoss?
Queris
What is a parameter queris?
a parameter query is a query that prompts the user to enter specific criteria every time the query is run. When building the query, you would enter the prompt in the criteria line under the field you want the information to be filtered from. For example, if you wanted to look at items that sold on a specific date each time you ran the query, your criteria line would look like this: [enter date of sale] So when you ran the query, before your results even appeared, a parameter box would pop up telling you "enter date of sale", the user would enter the date and then the filtered criteria of the query results will show.
