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| author | cmiller@zippy.cornsilk.net <> | 2006-12-22 15:59:10 -0500 |
|---|---|---|
| committer | cmiller@zippy.cornsilk.net <> | 2006-12-22 15:59:10 -0500 |
| commit | 83355bfb8104215fe6d0f699e55977f4a1760545 (patch) | |
| tree | 660058307773737acf114594612f03b8754edb03 /sql/item_sum.h | |
| parent | 7d07c33d3055392e626d9d12ff947a092f2b460c (diff) | |
| parent | 50726b2322edac8e93489fcb5ef75a5634222d44 (diff) | |
| download | mariadb-git-83355bfb8104215fe6d0f699e55977f4a1760545.tar.gz | |
Merge zippy.cornsilk.net:/home/cmiller/work/mysql/bug22555/my50-bug22555
into zippy.cornsilk.net:/home/cmiller/work/mysql/bug22555/my51-bug22555
Diffstat (limited to 'sql/item_sum.h')
| -rw-r--r-- | sql/item_sum.h | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/sql/item_sum.h b/sql/item_sum.h index eb4c21bbe06..8929e3d8fde 100644 --- a/sql/item_sum.h +++ b/sql/item_sum.h @@ -665,8 +665,10 @@ public: double val_real(); longlong val_int() { /* can't be fix_fields()ed */ return (longlong) rint(val_real()); } - String *val_str(String*); - my_decimal *val_decimal(my_decimal *); + String *val_str(String *str) + { return val_string_from_real(str); } + my_decimal *val_decimal(my_decimal *dec_buf) + { return val_decimal_from_real(dec_buf); } bool is_null() { (void) val_int(); return null_value; } enum_field_types field_type() const { @@ -688,6 +690,14 @@ public: = (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) + +But, this falls prey to catastrophic cancellation. Instead, use the recurrence formulas + + M_{1} = x_{1}, ~ M_{k} = M_{k-1} + (x_{k} - M_{k-1}) / k newline + S_{1} = 0, ~ S_{k} = S_{k-1} + (x_{k} - M_{k-1}) times (x_{k} - M_{k}) newline + for 2 <= k <= n newline + ital variance = S_{n} / (n-1) + */ class Item_sum_variance : public Item_sum_num @@ -696,9 +706,8 @@ class Item_sum_variance : public Item_sum_num public: Item_result hybrid_type; - double sum, sum_sqr; - my_decimal dec_sum[2], dec_sqr[2]; int cur_dec; + double recurrence_m, recurrence_s; /* Used in recurrence relation. */ ulonglong count; uint f_precision0, f_scale0; uint f_precision1, f_scale1; @@ -707,7 +716,7 @@ public: uint prec_increment; Item_sum_variance(Item *item_par, uint sample_arg) :Item_sum_num(item_par), - hybrid_type(REAL_RESULT), cur_dec(0), count(0), sample(sample_arg) + hybrid_type(REAL_RESULT), count(0), sample(sample_arg) {} Item_sum_variance(THD *thd, Item_sum_variance *item); enum Sumfunctype sum_func () const { return VARIANCE_FUNC; } @@ -727,7 +736,6 @@ public: enum Item_result result_type () const { return REAL_RESULT; } void cleanup() { - cur_dec= 0; count= 0; Item_sum_num::cleanup(); } |