Opened 8 years ago

Last modified 7 years ago

#1557 closed enhancement

stddev / var condensers — at Initial Version

Reported by: Dimitar Misev Owned by:
Priority: major Milestone: 9.5
Component: qlparser Version: development
Keywords: Cc: Peter Baumann, bbell, Vlad Merticariu
Complexity: Medium

Description

SQL and various array DBMS support standard deviation and variance aggregations. Quoting from the SQL standard:

  • If VAR_POP is specified, then the population variance of <value expression> evaluated for each row that

qualifies, defined as the sum of squares of the difference of <value expression> from the mean of <value
expression>, divided by the number of rows that qualify.

  • If VAR_SAMP is specified, then the sample variance of <value expression> evaluated for each row that

qualifies, defined as the sum of squares of the difference of <value expression> from the mean of <value
expression>, divided by the number of rows that qualify minus 1 (one).

  • If STDDEV_POP is specified, then the population standard deviation of <value expression> evaluated for

each row that qualifies, defined as the square root of the population variance.

  • If STDDEV_SAMP is specified, then the sample standard deviation of <value expression> evaluated for

each row that qualifies, defined as the square root of the sample variance.

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