DBMS: Query Plan (Definitions)

"The ordered set of steps required to carry out a query, complete with the access methods chosen for each table." (Karen Paulsell et al, "Sybase SQL Server: Performance and Tuning Guide", 1996)

"A portion of a DBMS that determines the most efficient sequence of relational algebra operations to use to satisfy a query." (Jan L Harrington, "Relational Database Design and Implementation" 3rd Ed., 2009)

"The plan produced by an optimizer for processing a query." (S. Sumathi & S. Esakkirajan, "Fundamentals of Relational Database Management Systems", 2007)

"A query plan is a sequence of logical and physical operators and data flows that the SQL query optimizer returns for use by the query processor to retrieve or modify data." (Michael Coles, "Pro T-SQL 2008 Programmer's Guide", 2008)

"Once the query optimizer determines the best way to execute a query, it creates a query plan. This identifies all the elements of the query, including what indexes are used, what types of joins are employed, and more." (Darril Gibson, "MCITP SQL Server 2005 Database Developer All-in-One Exam Guide", 2008)

"A sequence of logical and physical operators and data flows that the SQL query optimizer returns for use by the query processor to retrieve or modify data." (Miguel Cebollero et al, "Pro T-SQL Programmer’s Guide" 4th Ed., 2015)

[adaptive query plan:] "An execution plan that changes after optimization because run-time conditions indicate that optimizer estimates are inaccurate. An adaptive query plan has different built-in plan options. During the first execution, before a specific subplan becomes active, the optimizer makes a final decision about which option to use. The optimizer bases its choice on observations made during the execution up to this point. Thus, an adaptive query plan enables the final plan for a statement to differ from the default plan." (Oracle)

[default plan:] "For an adaptive plan, the execution plan initially chosen by the optimizer using the statistics from the data dictionary. The default plan can differ from the final plan." (Oracle)

[execution plan:] "The combination of steps used by the database to execute a SQL statement. Each step either retrieves rows of data physically from the database or prepares them for the session issuing the statement." (Oracle)

[query execution plan:] "The set of decisions made by the optimizer about how to perform a query most efficiently, including which index or indexes to use, and the order in which to join tables." (MySQL)