Query processing It is a process of transforming a high level query (such as SQL) in to low level language. Query processing refers to the range of activities involved in extracting data from a database. A query expressed in a high level query language such as SQL must be Scanned Parsed Validated The scanner identifies the language tokens such as SQL keywords, attribute names and relation names in the text of the query. Parser checks the query syntax to determine whether it is formulated according to the syntax rules of the query language. The query must also be validated by checking that all attributes and relation names are valid and semantically meaningful names in the schema of the particular database being queried. A query typically has many possible execution strategies and the process of choosing a suitable one for processing a query is known as query optimization. The query optimizer module has the task of producing an execution plan and code generator generates the code to execute that plan. The runtime database processor has the task of running the query code whether in compiled or interpreted mode, to produce the query result. If a runtime error results, an error message is generated by the runtime database processor. Query code generator will generate code for query. Runtime database processor will select optimal plan and execute query and gives result.
