Foreign Key Definition A foreign key is a column or columns of data in one table that connects to the primary key data in the original table. To ensure the links between foreign key and primary key tables aren't broken, foreign key constraints can be created to prevent actions that would damage the links between tables and prevent erroneous data from being added to the foreign key column. Differences between primary and foreign keys A primary key in the original table, or parent table, c...

Trigger Definition   A trigger (from the Dutch trekken, meaning to pull) is a lever which, when pulled by the finger, releases the hammer on a firearm. In a database, a trigger is a set of Structured Query Language (SQL) statements that automatically "fires off" an action when a specific operation, such as changing data in a table, occurs. A trigger consists of an event (an INSERT, DELETE, or UPDATE statement issued against an associated table) and an action (the related procedure). T...

SQL-on-Hadoop SQL-on-Hadoop is a class of analytical application tools that combine established SQL-style querying with newer Hadoop data framework elements. By supporting familiar SQL queries, SQL-on-Hadoop lets a wider group of enterprise developers and business analysts work with Hadoop on commodity computing clusters. Because SQL was originally developed for relational databases, it has to be modified for the Hadoop 1 model, which uses the Hadoop Distributed File System and Map-Reduce or...

T-SQL (Transact-SQL) T-SQL (Transact-SQL) is a set of programming extensions from Sybase and Microsoft that add several features to the Structured Query Language (SQL), including transaction control, exception and error handling, row processing and declared variables. All applications that communicate with SQL Server do so by sending T-SQL statements to the server. T-SQL queries include the SELECT statement, selecting columns, labeling output columns, restricting rows and modifying a search ...

PL/SQL (procedural language extension to Structured Query Language) In Oracle database management, PL/SQL is a procedural language extension to Structured Query Language (SQL). The purpose of PL/SQL is to combine database language and procedural programming language. The basic unit in PL/SQL is called a block, which is made up of three parts: a declarative part, an executable part, and an exception-building part. Because PL/SQL allows you to mix SQL statements with procedural construct...