Lo que todo programador debería saber sobre aritmética de punto flotante
fixed issue #2 - Add language section for SQL
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---
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title: Floating-point cheat sheet for SQL
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description: Tips for using floating-point and decimal numbers in SQL
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---
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Floating-Point Types
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--------
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The SQL standard defines three binary floating-point types:
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* `REAL` has implementation-dependant precision (usually maps to a hardware-supported type like IEEE 754 single or double precision)
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* `DOUBLE PRECISION` has implementation-dependant precision which is greater than `REAL` (usually maps to IEEE 754 double precision)
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* `FLOAT(N)` has at least `N` binary digits of precision, with an implementation-dependant maximum for `N`
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The exponent range for all three types is implementation-dependant as well.
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Decimal Types
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-------------
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The standard defines two fixed-point decimal types:
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* `NUMERIC(M,N)` has exactly `M` total digits, `N` of them after the decimal point
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* `DECIMAL(M,N)` is the same as `NUMERIC(M,N)`, except that it is allowed to have more than `M` total digits
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The maximum values of `M` and `M` are implementation-dependant. Vendors often implement the two types identically.
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How to Round
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------------
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The SQL standard defines no explicit rounding, but most vendors provide a `ROUND()` or `TRUNC()` function.
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However, it usually makes little sense to round within the database, since its job is *storing* data, while rounding is an aspect of *displaying* data, and should therefore be done by the code in the presentation layer.
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Resources
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---------
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* [Official ISO SQL 2008 standard (non-free)](http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=38640)
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* [SQL 92 draft (free)](http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt)
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* [MySQL numeric types](http://dev.mysql.com/doc/refman/5.0/en/numeric-types.html)
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* [PostgreSQL data types](http://www.postgresql.org/docs/8.1/static/datatype.html)
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* [MS SQL Server data types](http://msdn.microsoft.com/en-US/library/ms187752%28v=SQL.90%29.aspx)
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<li><a href="/languages/java/">Java</a></li>
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<li><a href="/languages/javascript/">JavaScript</a></li>
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<li><a href="/languages/php/">PHP</a></li>
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<li><a href="/languages/sql/">SQL</a></li>
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</ul>
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</div>
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<a href="http://github.com/brazzy/floating-point-gui.de"><img style="position: absolute; top: 0; right: 0; border: 0;" src="http://s3.amazonaws.com/github/ribbons/forkme_right_white_ffffff.png" alt="Fork me on GitHub" /></a>