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The performance of a query plan is determined largely by the order in which the tables are joined. For example, when joining 3 tables A, B, C of size 10 rows, 10,000 rows, and 1,000,000 rows, respectively, a query plan that joins B and C first can take several orders-of-magnitude more time to execute than one that joins A and C first.
Since SQL is declarative, there are typically many alternative ways to execute a given query, with widely varying performance. When a query is submitted to the database, the query optimizer evaluates some of the different, correct possible plans for executing the query and returns what it considers the best option.
Database tuning describes a group of activities used to optimize and homogenize the performance of a database.It usually overlaps with query tuning, but refers to design of the database files, selection of the database management system (DBMS) application, and configuration of the database's environment (operating system, CPU, etc.).
SQL Performance Tuning by Peter Gulutzan, Trudy Pelzer (Addison Wesley, 2002) ISBN 0-201-79169-2 (Chapter 2, Simple "Searches"); Microsoft SQL Server 2012 Internals by Kalen Delaney, Connor Cunningham, Jonathan Kehayias, Benjamin Nevarez, Paul S. Randal (O'Reily, 2013) ISBN 978-0-7356-5856-1 (Chapter 11, The Query Optimizer)
Database normalization is the process of structuring a relational database accordance with a series of so-called normal forms in order to reduce data redundancy and improve data integrity.
Many informal performance studies of PostgreSQL have been done. [81] Performance improvements aimed at improving scalability began heavily with version 8.1. Simple benchmarks between version 8.0 and version 8.4 showed that the latter was more than ten times faster on read-only workloads and at least 7.5 times faster on both read and write ...
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The SQL specification defines what an "SQL schema" is; however, databases implement it differently. To compound this confusion the functionality can overlap with that of a parent database. An SQL schema is simply a namespace within a database; things within this namespace are addressed using the member operator dot ".". This seems to be a ...