Compilers of SQL language Lecture 18. Compilers SQL. Optimization problems

Speaking about query optimization in relational DBMS, they usually mean this way of query processing, when according to the initial presentation of a query by its transformations, a procedural plan of its execution is developed, the most optimal with the control structures existing in the database. The corresponding transformations of the initial representation of the query are performed by a special component of the DBMS - the optimizer, and the optimality of the query plan produced by it is conditional: the plan is optimal in accordance with the criteria laid down in the optimizer