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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. Because query optimizers are ...
Oracle PL/SQL for DBAs, First Edition, O'Reilly Media, October 2005, ISBN 0-596-00587-3; with Guy Harrison. MySQL Stored Procedure Programming: Building High-Performance Web Applications in MySQL, O'Reilly Media, March 2006, ISBN 0-596-10089-2; Oracle PL/SQL Best Practices, Second Edition, O'Reilly Media, October 2007, ISBN 0-596-51410-7
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.
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.).
In the field of software, SQL programming tools provide platforms for database administrators (DBAs) and application developers to perform daily tasks efficiently and accurately. Database administrators and application developers often face constantly changing environments which they rarely completely control.
ISO/IEC 9075 "Information technology - Database languages - SQL" is an international standard for Structured Query Language, and is considered as specifying the minimum for what a database engine should fulfill in terms of SQL syntax, which is called Core SQL. The standard also defines a number of optional features.
Azure SQL Database includes built-in intelligence that learns app patterns and adapts them to maximize performance, reliability, and data protection. Key capabilities include: Learning of the host app's data access patterns, adaptive performance tuning, and automatic improvements to reliability and data protection. [3] Scaling on demand. [4]
In databases, and transaction processing (transaction management), snapshot isolation is a guarantee that all reads made in a transaction will see a consistent snapshot of the database (in practice it reads the last committed values that existed at the time it started), and the transaction itself will successfully commit only if no updates it has made conflict with any concurrent updates made ...
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