lekérdezéstervek

lekérdezéstervek (Hungarian for "query plans") are the sequences of operations a database management system (DBMS) decides to execute to retrieve data from a database. When a user or application submits a query, the DBMS doesn't immediately start fetching data. Instead, it employs a query optimizer, a component responsible for determining the most efficient way to execute the query. The query plan is the output of this optimization process.

A query plan outlines the specific access methods, join strategies, and order of operations that the DBMS will follow. For example, it might specify whether to use an index to find records, which join algorithm (like a nested loop join, hash join, or merge join) to employ for combining tables, and the order in which to perform these operations. The goal is to minimize resource consumption, such as CPU time, I/O operations, and memory usage, thereby speeding up query execution.

Different query plans can exist for the same SQL statement, and the optimizer selects the one it estimates to be the fastest based on database statistics, such as table sizes and index selectivity. Understanding query plans is crucial for database administrators and developers when troubleshooting performance issues or optimizing complex queries. Most DBMS provide tools to display and analyze the execution plan of a query.