Kyselykääntäjä

Kyselykääntäjä is a Finnish term that translates to "query translator" or "query compiler" in English. It refers to a component or process within a database management system or a data processing framework responsible for converting a user-written query into a form that the system can efficiently execute. This process typically involves parsing the query, analyzing its structure and meaning, and then optimizing it for performance.

The primary function of a kyselykääntäjä is to take a high-level query, often expressed in a declarative language like SQL, and transform it into a sequence of low-level operations that the database engine can understand and perform. This transformation can involve several steps, including syntax checking, semantic analysis, and query optimization. Syntax checking ensures that the query adheres to the rules of the query language. Semantic analysis verifies that the query refers to valid database objects like tables and columns and that the operations are logically sound.

Query optimization is a crucial part of the kyselykääntäjä's role. The optimizer considers various execution plans for a given query and selects the one that is estimated to be the most efficient, minimizing resource usage such as CPU time and disk I/O. This might involve choosing different join algorithms, table access methods, or reordering operations. The output of the kyselykääntäjä is typically an executable query plan that the database's execution engine then carries out.