diff options
| author | unknown <vva@eagle.mysql.r18.ru> | 2002-12-14 04:53:28 +0400 |
|---|---|---|
| committer | unknown <vva@eagle.mysql.r18.ru> | 2002-12-14 04:53:28 +0400 |
| commit | 19f6ad06c04474abecca0cca3d6bd143fb712c45 (patch) | |
| tree | f16b7fdebf7d1dce7a6d2aecb3564d9e766fb844 /sql/item_sum.h | |
| parent | 29624e3212d93fbd0b0d741e5a000b7b64ce83e0 (diff) | |
| download | mariadb-git-19f6ad06c04474abecca0cca3d6bd143fb712c45.tar.gz | |
fix stupid error in comments to VARIANCE+STD
Diffstat (limited to 'sql/item_sum.h')
| -rw-r--r-- | sql/item_sum.h | 20 |
1 files changed, 12 insertions, 8 deletions
diff --git a/sql/item_sum.h b/sql/item_sum.h index 442366ee35b..b5665c3cf8c 100644 --- a/sql/item_sum.h +++ b/sql/item_sum.h @@ -255,15 +255,15 @@ public: variance(a) = -= sqrt ( sum (ai - avg(a))^2 / count(a) ) -= sqrt ( sum (ai^2 - 2*ai*avg(a) + avg(a)^2) / count(a) ) -= sqrt ( (sum(ai^2) - sum(2*ai*avg(a)) + sum(avg(a)^2))/count(a) ) = -= sqrt ( (sum(ai^2) - 2*avg(a)*sum(a) + count(a)*avg(a)^2)/count(a) ) = -= sqrt ( (sum(ai^2) - 2*sum(a)*sum(a)/count(a) + count(a)*sum(a)^2/count(a)^2 )/count(a) ) = -= sqrt ( (sum(ai^2) - 2*sum(a)^2/count(a) + sum(a)^2/count(a) )/count(a) ) = -= sqrt ( (sum(ai^2) - sum(a)^2/count(a))/count(a) ) += sum (ai - avg(a))^2 / count(a) ) += sum (ai^2 - 2*ai*avg(a) + avg(a)^2) / count(a) += (sum(ai^2) - sum(2*ai*avg(a)) + sum(avg(a)^2))/count(a) = += (sum(ai^2) - 2*avg(a)*sum(a) + count(a)*avg(a)^2)/count(a) = += (sum(ai^2) - 2*sum(a)*sum(a)/count(a) + count(a)*sum(a)^2/count(a)^2 )/count(a) = += (sum(ai^2) - 2*sum(a)^2/count(a) + sum(a)^2/count(a) )/count(a) = += (sum(ai^2) - sum(a)^2/count(a))/count(a) - */ +*/ class Item_sum_variance : public Item_sum_num { @@ -294,6 +294,10 @@ public: double val(); }; +/* + standard_deviation(a) = sqrt(variance(a)) +*/ + class Item_sum_std :public Item_sum_variance { public: |