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Query by Example. 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.
This is a list of TCP and UDP port numbers used by protocols for operation of network applications. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) only need one port for duplex, bidirectional traffic.
In SQL:1999 a recursive (CTE) query may appear anywhere a query is allowed. It's possible, for example, to name the result using CREATE [RECURSIVE] VIEW. Using a CTE inside an INSERT INTO, one can populate a table with data generated from a recursive query; random data generation is possible using this technique without using any procedural ...
In data managementand data warehousing, a slowly changing dimension(SCD) is a dimensionthat stores datawhich, while generally stable, may change over time, often in an unpredictable manner.[1] This contrasts with a rapidly changing dimension, such as transactional parameters like customer ID, product ID, quantity, and price, which undergo ...
Database normalization is the process of structuring a relational database in accordance with a series of so-called normal forms in order to reduce data redundancy and improve data integrity. It was first proposed by British computer scientist Edgar F. Codd as part of his relational model . Normalization entails organizing the columns ...
In computing, SQL injection is a code injection technique used to attack data-driven applications, in which malicious SQL statements are inserted into an entry field for execution (e.g. to dump the database contents to the attacker). [ 1][ 2] SQL injection must exploit a security vulnerability in an application's software, for example, when ...
Correlated subquery. In a SQL database query, a correlated subquery (also known as a synchronized subquery) is a subquery (a query nested inside another query) that uses values from the outer query. Because the subquery may be evaluated once for each row processed by the outer query, it can be slow.
A non-primary key that can be used to identify only one row in a table. Alternate keys may be used like a primary key in a single-table select. Foreign. A key that has migrated to another entity. At the most basic definition, "a key is a unique identifier", [1] so unique key is a pleonasm. Keys that are within their originating entity are ...