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Oracle implements hints by using specially-crafted comments in the query that begin with a + symbol, thus not affecting SQL compatibility. [2] EDB Postgres Advanced Server (a proprietary version of PostgreSQL from EnterpriseDB) offers hints compatible with those of Oracle. [3] [4] Microsoft SQL Server offers hints via the OPTION keyword [5]
Some query tools can generate embedded hints in the query, for use by the optimizer. Some databases - like Oracle - provide a plan table for query tuning. This plan table will return the cost and time for executing a query. Oracle offers two optimization approaches: CBO or Cost Based Optimization; RBO or Rule Based Optimization
The RFC specifies this code should be returned by teapots requested to brew coffee. [18] This HTTP status is used as an Easter egg in some websites, such as Google.com's "I'm a teapot" easter egg. [19] [20] [21] Sometimes, this status code is also used as a response to a blocked request, instead of the more appropriate 403 Forbidden. [22] [23]
In cryptography, a message authentication code (MAC), sometimes known as an authentication tag, is a short piece of information used for authenticating and integrity-checking a message. In other words, to confirm that the message came from the stated sender (its authenticity) and has not been changed (its integrity).
The query optimizer attempts to determine the most efficient way to execute a given query by considering the possible query plans. [ 1 ] Generally, the query optimizer cannot be accessed directly by users: once queries are submitted to the database server, and parsed by the parser, they are then passed to the query optimizer where optimization ...
PL/SQL refers to a class as an "Abstract Data Type" (ADT) or "User Defined Type" (UDT), and defines it as an Oracle SQL data-type as opposed to a PL/SQL user-defined type, allowing its use in both the Oracle SQL Engine and the Oracle PL/SQL engine. The constructor and methods of an Abstract Data Type are written in PL/SQL.
A query includes a list of columns to include in the final result, normally immediately following the SELECT keyword. An asterisk ("*") can be used to specify that the query should return all columns of the queried tables. SELECT is the most complex statement in SQL, with optional keywords and clauses that include:
Query by Example (QBE) is a database query language for relational databases. It was devised by Moshé M. Zloof at IBM Research during the mid-1970s, in parallel to the development of SQL . [ 1 ] It is the first graphical query language, using visual tables where the user would enter commands, example elements and conditions.