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tables. In a database, a query is the request for information from a database table. Query is a database query, a search or inquiry, a request or



 

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A query is the inquiry, request, and search for information. A query may be a request for information from a database table or combination of tables. In a database, a query is the request for information from a database table. Query is a database query, a search or inquiry, a request or inquiry. published:22 Jun 2017 views:49 6:29 What Are Queries? What Are Queries? What Are Queries? published:22 Jun 2017 views:99 A query is a specific request for information from a database. In robust database systems in particular, queries make it easier to perceive information they need to carry out their tasks. In modern database systems, the job of a query engine is to accept queries from a user or application and to return to them answers in a form that the user or application can understand. Query processing, then, takes two main forms: interpretation and execution. Interpretation refers to parsing and understanding the structure of the query. Execution refers to doing a search for requested information using the results of the query interpretation. The result of this search is called the answer set. Answering a query involves finding the answer set. In this video, we explain the concepts of query interpretation and the various phases involved in query processing. A simple query, such as one that retrieves the names of all the cities in the United States, is an example of a query that retrieves information from a database. 1. Parsing Parsing is the process of analyzing the syntax of the query so that its structure may be understood. One step in parsing is analyzing the words and phrases that make up the query. A query like "all the cities in California" contains several words and phrases: cities, in, California. Each of these words and phrases, or lexical items, requires analysis and interpretation. Once the lexical items have been determined, the structural elements that describe the relationship between the words and phrases can be identified. In the case of the previous query, California would be considered a predicate (a word or phrase that describes or modifies some other word or phrase) and cities, in, would be considered a determiner (a word or phrase that provides additional information about the noun or noun phrase that it precedes). In general, the rules that govern the syntax of




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