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Each Federated table that is defined there is one .frm (data definition file containing information such as the URL of the data source). The actual data can exist on a local or remote Oracle, Microsoft SQL Server (MSSQL), or MySQL instance. To create a Federated table, one has to specify a URL in the "CONNECTION" string:
SQL allows triggers to fire on updates to specific columns; As of version 9.0 of PostgreSQL this feature is also implemented in PostgreSQL. The standard allows the execution of a number of SQL statements other than SELECT, INSERT, UPDATE, such as CREATE TABLE as the triggered action. This can be done through creating a stored procedure or ...
A hierarchical query is a type of SQL query that handles hierarchical model data. They are special cases of more general recursive fixpoint queries, which compute transitive closures. In standard SQL:1999 hierarchical queries are implemented by way of recursive common table expressions (CTEs).
If the "child" data type were different, it would be in a different table, but there would still be a foreign key referencing the EmpNo column of the employees table. This simple model is commonly known as the adjacency list model and was introduced by Dr. Edgar F. Codd after initial criticisms surfaced that the relational model could not model ...
The basic data structure of the relational model is the table, where information about a particular entity (say, an employee) is represented in rows (also called tuples) and columns. Thus, the "relation" in "relational database" refers to the various tables in the database; a relation is a set of tuples. The columns enumerate the various ...
A database engine (or storage engine) is the underlying software component that a database management system (DBMS) uses to create, read, update and delete (CRUD) data from a database. Most database management systems include their own application programming interface (API) that allows the user to interact with their underlying engine without ...
In the context of SQL, data definition or data description language (DDL) is a syntax for creating and modifying database objects such as tables, indices, and users. DDL statements are similar to a computer programming language for defining data structures, especially database schemas. Common examples of DDL statements include CREATE, ALTER ...
Each column in an SQL table declares the type(s) that column may contain. ANSI SQL includes the following data types. [14] Character strings and national character strings. CHARACTER(n) (or CHAR(n)): fixed-width n-character string, padded with spaces as needed; CHARACTER VARYING(n) (or VARCHAR(n)): variable-width string with a maximum size of n ...