Algebraic Optimization

Same as: SQL Engine - Query Optimizer (Query Optimization)

<MATH> N = ((Z*2)+((Z*3)+0))/1 </MATH>

Algebraic Laws:

1. (+) identity: x+0 = x
2. (/) identity: x/1 = x
3. (*) distributes: (n*x+n*y) = n*(x+y)
4. (*) commutes: x*y = y*x

Apply rules 1,3,4,2 and we get <MATH> N = (2+3)*z </MATH>

Two operations instead of five, no division operator

Same idea works with the Relational Algebra

Filter Early is an algebraic optimization:

Predicate push Down is the same that filter early.

It is valid to push a filter into an input of an inner join if the filter does not reference columns from the other input.

• Column pruning

Example from CALCITE-873

Given the following table:

CREATE TABLE T (
  K1 VARCHAR,
  K2 VARCHAR,
  K3 VARCHAR,
  CONSTRAINT pk PRIMARY KEY (K1, K2, K3));

In the following queries, no sort is necessary:

SELECT * FROM T WHERE K1='A' ORDER BY K2,K3;
SELECT * FROM T WHERE K2='B' ORDER BY K1,K3;
SELECT * FROM T WHERE K1='A' AND K2='B' ORDER BY K3;

• https://blogs.oracle.com/datawarehousing/big-data-sql-quick-start-predicate-push-down-part6