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Query rewriting is a typically automatic transformation that takes a set of database tables, views, and/or queries, usually indices, often gathered data and query statistics, and other metadata, and yields a set of different queries, which produce the same results but execute with better performance (for example, faster, or with lower memory use). [1]
SQL includes operators and functions for calculating values on stored values. SQL allows the use of expressions in the select list to project data, as in the following example, which returns a list of books that cost more than 100.00 with an additional sales_tax column containing a sales tax figure calculated at 6% of the price.
This template displays one or more of a template's shortcuts (that is, redirects, also known as aliases), as in the box appearing at the right. {{ Tsh }} is a shortcut to this template, {{template shortcut}} , and can be used in its place, as it is in this documentation's source wikitext .
The shortcut family of templates is put into context here, but they each have their own documentation pages, see below. A shortcut template is similar to the {} template, but it adds a visual box graphic to the rendered page, as well as providing an alternative name. Creating a redirect page is a requirement to fulfill the shortcut mechanism.
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.
The grid method (or box method) is an introductory method for multiple-digit multiplication that is often taught to pupils at primary school or elementary school. It has been a standard part of the national primary school mathematics curriculum in England and Wales since the late 1990s.
For this example it is assumed that each book has only one author. A table that conforms to the relational model has a primary key which uniquely identifies a row. In our example, the primary key is a composite key of {Title, Format} (indicated by the underlining):
Here is a more advanced example, showing some more options available for making up tables. Users can play with these settings in their own table to see what effect they have. Not all of these techniques may be appropriate in all cases; just because colored backgrounds can be added, for example, does not mean it is always a good idea.