1. ONE PASS ALGORITHM PRESENTED BY: PRADHYUMAN RAOL ID : 114 Instructor: Dr T.Y. LIN

2. Agenda  One Pass algorithm  Tuple-at-a-Time  Unary Operators  Binary Operations

3. One-Pass Algorithms  One Pass Algorithm:  Some methods involve reading the data only once from disk.  They work only when at least one of the arguments of the operation fits in main memory.

4. Tuple-at-a-Time  We read the blocks of R one at a time into an input buffer, perform the operation on the tuple, and more the selected tuples or the projected tuples to the output buffer.  Examples: Selection & Projection

5. Tuple at a time Diagram Input bufferOutput buffer Unary operator R

6. Unary Operators  The unary operations that apply to relations as a whole, rather than to one tuple at a time.  Duplicate Elimination  (R) :Check whether that tuple is already there or not. M= Main memory B(  (R))= Size of Relation R Assumption: B(  (R)) <= M

7. Unary Operators  Grouping : A grouping operation gives us zero or more grouping attributes and presumably one or more accumulated value or values for each aggregation.  Min or Max  Count  Sum  Average

8. Binary Operations  Set Union  Set Intersection  Set Difference  Bag Intersection  Bag Difference  Product  Natural join

9. Thank You