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This article mainly introduces "the advantages of query optimization of SQL". In daily operation, I believe that many people have doubts about the advantages of query optimization of SQL. The editor consulted all kinds of data and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts of "the advantages of query optimization of SQL". Next, please follow the editor to study!

Advantages of query optimization

1. Users do not have to consider how best to express the query to achieve better efficiency

2. The system can do better than the "optimization" of the user program.

Algebraic optimization, according to certain rules, through the equivalent transformation of relational algebraic expressions to change the order and combination of operations in algebraic expressions, so as to make query execution more efficient. There are many formulas.

1. Law of connection and Cartesian product exchange

two。 The associative law of connection and Cartesian product

Physical optimization is to choose an efficient and reasonable operation algorithm or access path to obtain an optimized query plan.

1) Rule-based heuristic optimization

Heuristic rules are those that apply in most cases, but not the best in every case.

2) Optimization based on cost estimation

The optimizer estimates the cost of different execution strategies and selects the execution plan with the lowest cost.

3) the optimization method of the combination of both:

Heuristic rules are often used first to select some better candidates to reduce the workload of cost estimation.

At this point, the study on "the advantages of query optimization of SQL" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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