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MySQL uses a .frm file to store the definition of the table, but this file is not a part of the MyISAM engine; instead it is a part of the server. The data file has a .MYD (MYData) extension. The index file has a .MYI (MYIndex) extension. The index file, if lost, can always be recreated by recreating indexes.
For a trivial hash function lookup, the unsigned raw data value is used directly as an index to a one-dimensional table to extract a result. For small ranges, this can be amongst the fastest lookup, even exceeding binary search speed with zero branches and executing in constant time. [6]
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 .
Note (5): InnoDB automatically generates adaptive hash index [125] entries as needed. Note (6): Can be implemented using Function-based Indexes in Oracle 8i and higher, but the function needs to be used in the sql for the index to be used. Note (7): A PostgreSQL functional index can be used to reverse the order of a field.
No two distinct rows or data records in a database table can have the same data value (or combination of data values) in those candidate key columns since NULL values are not used. Depending on its design, a database table may have many candidate keys but at most one candidate key may be distinguished as the primary key.
Consider an example from the expression language found in Microsoft_excel. Excel can calculate a cell's value dynamically by typing an expression such as "=SUM(C5:C10)", which performs the arithmetic sum of those 6 cells. The expression language in Ignition functions similarly. It is used to define dynamic values for tags and component properties.
A pivot table is a table of values which are aggregations of groups of individual values from a more extensive table (such as from a database, spreadsheet, or business intelligence program) within one or more discrete categories. The aggregations or summaries of the groups of the individual terms might include sums, averages, counts, or other ...
Because Excel is widely used, it has been attacked by hackers. While Excel is not directly exposed to the Internet, if an attacker can get a victim to open a file in Excel, and there is an appropriate security bug in Excel, then the attacker can gain control of the victim's computer. [121] UK's GCHQ has a tool named TORNADO ALLEY with this purpose.