Opened 2 weeks ago

Last modified 2 weeks ago

## #1557 new enhancement

# stddev / var condensers

Reported by: | dmisev | Owned by: | |
---|---|---|---|

Priority: | major | Milestone: | 9.5 |

Component: | qlparser | Version: | development |

Keywords: | Cc: | pbaumann, bbell, vmerticariu | |

Complexity: | Medium |

### Description (last modified by dmisev)

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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