Aggregate. Returns the mean absolute deviation of a given expression over multiple rows. Absolute deviation is the mean of the absolute value of the deviations from the mean of all values.
Syntax
meandeviation ( numeric-expression )
Parameters
| numeric-expression | An expression, commonly a column name, for which the sample-based standard deviation is calculated over a set of rows. The expression will normally reference one or more columns in a group of records such that the mean deviation will be computed using the reference column value for each member of the group. |
Usage
This function converts the argument to float, performs the computation in double-precision floating point, and returns a float. The mean deviation is computed according to the following formula:
This mean deviation does not include rows where numeric-expression is NULL. It returns NULL for a group containing no rows.
The mean deviation function could be used for optimization of stock portfolios on a real-time basis.