Introduction

Introduction#

Query Parser#

The query first gets parsed:

  • Check for correctness and authorization

  • Generate a parse tree

Query Rewriter#

Rewrites query to its canonical form,

  • Flatten views

  • Subqueries into blocks

  • The weak spot of many DBMS

Query Optimizer#

Creates the plan and estimates the cost.

  • Per query block, the optimizer will use the least cost plan.

  • Query block can be converted to relational algebra.

  • Relational algebra to tree.

  • Each operator has a choice of implementation.

  • Operators can be applied in different orders.

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