The core components of a database query engine work together to interpret and execute user queries, enabling efficient data retrieval and manipulation. These components include:
- Lexer: The lexer, also known as a tokenizer, breaks down the user-entered query into individual tokens, such as keywords, operators, and identifiers. It separates the query into meaningful units for further processing.
- Parser: The parser analyzes the tokens identified by the lexer and constructs a parse tree, which represents the syntactic structure of the query. It checks the query for grammar and syntax errors to ensure it adheres to the database’s query language rules.
- Binder: The binder binds identifiers, such as table names and column names, to their corresponding entries in the database schema. It resolves aliases and ensures that the query references valid database objects.
- Optimizer: The optimizer determines the most efficient way to execute the query. It considers various factors, such as table sizes, indexes, and query execution plans, to minimize the time required to retrieve the desired data.
- Executor: The executor translates the optimized query plan into machine-executable code. It interacts with the database’s storage engine to fetch the relevant data from the database tables.
- Storage Engine: The storage engine manages the physical storage of data on disk or other storage devices. It provides efficient access to data blocks and handles data retrieval, insertion, and modification operations.
- Query Evaluator: The query evaluator processes the data retrieved from the storage engine and applies any necessary operations, such as filtering, sorting, or aggregation, as specified in the query. It transforms the raw data into the desired output format.
- Result Compiler: The result compiler formats the query results into a displayable format, such as a table or a chart. It presents the processed data in a user-friendly manner.