A DBMS has a query processing module that allows it to quickly return the result of queries over relations.
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The Query Processing Unit consists of 3 components:
- Parser: Translates queries into their simplest/equivalent forms,
- Optimiser: Tries to reduce the number of O accesses for the query by generate-and-testing possible query plans, which are strategies to return the query output.
- Plan Generator: Generates a possible query plane
- Plan Cost Estimator: Estimates the I/O cost of the generated plan, without actually carrying it out
- Plan Evaluator: Finds the best possible query plan
Parser
Optimiser
Plan Generator
See Query Plan