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UNION can be useful in data warehouse applications where tables are not perfectly normalized. [2] A simple example would be a database having tables sales2005 and sales2006 that have identical structures but are separated because of performance considerations. A UNION query could combine results from both tables.
The relational algebra uses set union, set difference, and Cartesian product from set theory, and adds additional constraints to these operators to create new ones.. For set union and set difference, the two relations involved must be union-compatible—that is, the two relations must have the same set of attributes.
Microsoft SQL Server Management Studio (SSMS) is a software application developed by Microsoft that is used for configuring, managing, and administering all components within Microsoft SQL Server. First launched with Microsoft SQL Server 2005, it is the successor to the Enterprise Manager in SQL 2000 or before.
In this case it is the DBMS software's responsibility to ensure that any redundant copies are kept consistent. This method is often implemented in SQL as indexed views (Microsoft SQL Server) or materialized views (Oracle, PostgreSQL). A view may, among other factors, represent information in a format convenient for querying, and the index ...
You can use CREATE PUBLIC SYNONYM dual FOR sysmaster: "informix". sysdual to create a name dual in the current database with the same functionality. Microsoft Access: A table named DUAL may be created and the single-row constraint enforced via ADO (Table-less UNION query in MS Access) Microsoft SQL Server: SQL Server does not require a dummy ...
SQL, ODBC, JDBC, ADO.NET, Embedded SQL, C, C++, Python Proprietary Mimer SQL is a general purpose relational database server that can be configured to run fully in-memory. Mimer SQL has full ACID support, support for stored procedures and is the only database that has a full score on SQL compliance Mnesia: Ericsson: 2014 Open Source Erlang License
A SELECT statement retrieves zero or more rows from one or more database tables or database views. In most applications, SELECT is the most commonly used data manipulation language (DML) command. As SQL is a declarative programming language, SELECT queries specify a result set, but do not specify how to calculate it.
Views take very little space to store; the database contains only the definition of a view, not a copy of all the data that it presents. Views structure data in a way that classes of users find natural and intuitive. [2] Just as a function (in programming) can provide abstraction, so can a database view. In another parallel with functions ...