decode_histogram fixed to show delta of the last value with maximum.

mysql-test/r/statistics.result

@@ -1448,7 +1448,7 @@ avg_frequency	2.7640
 hist_size	100
 hist_type	SINGLE_PREC_HB
 hex(histogram)	0000000000000000000000000101010101010101010202020303030304040404050505050606070707080809090A0A0B0C0D0D0E0E0F10111213131415161718191B1C1E202224292A2E33373B4850575F6A76818C9AA7B9C4CFDADFE5EBF0F4F8FAFCFF
-decode_histogram(histogram,hist_type)	0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.004,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.004,0.000,0.000,0.004,0.000,0.000,0.000,0.004,0.000,0.000,0.000,0.004,0.000,0.000,0.000,0.004,0.000,0.004,0.000,0.000,0.004,0.000,0.004,0.000,0.004,0.000,0.004,0.004,0.004,0.000,0.004,0.000,0.004,0.004,0.004,0.004,0.004,0.000,0.004,0.004,0.004,0.004,0.004,0.004,0.008,0.004,0.008,0.008,0.008,0.008,0.020,0.004,0.016,0.020,0.016,0.016,0.051,0.031,0.027,0.031,0.043,0.047,0.043,0.043,0.055,0.051,0.071,0.043,0.043,0.043,0.020,0.024,0.024,0.020,0.016,0.016,0.008,0.008,0.012
+decode_histogram(histogram,hist_type)	0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.004,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.004,0.000,0.000,0.004,0.000,0.000,0.000,0.004,0.000,0.000,0.000,0.004,0.000,0.000,0.000,0.004,0.000,0.004,0.000,0.000,0.004,0.000,0.004,0.000,0.004,0.000,0.004,0.004,0.004,0.000,0.004,0.000,0.004,0.004,0.004,0.004,0.004,0.000,0.004,0.004,0.004,0.004,0.004,0.004,0.008,0.004,0.008,0.008,0.008,0.008,0.020,0.004,0.016,0.020,0.016,0.016,0.051,0.031,0.027,0.031,0.043,0.047,0.043,0.043,0.055,0.051,0.071,0.043,0.043,0.043,0.020,0.024,0.024,0.020,0.016,0.016,0.008,0.008,0.012,0.000
 select db_name,table_name,column_name,min_value,max_value,nulls_ratio,avg_length,avg_frequency,hist_size,hist_type,hex(histogram),decode_histogram(histogram,hist_type) from mysql.column_stats where table_name='City' and column_name = 'Population';;
 db_name	world
 table_name	City
@@ -1473,7 +1473,7 @@ avg_frequency	1.0467
 hist_size	254
 hist_type	DOUBLE_PREC_HB
 hex(histogram)	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
-decode_histogram(histogram,hist_type)	0.00047,0.00198,0.00601,0.00008,0.00008,0.00005,0.00011,0.00006,0.00009,0.00008,0.00006,0.00009,0.00008,0.00009,0.00008,0.00009,0.00006,0.00006,0.00008,0.00008,0.00008,0.00011,0.00009,0.00008,0.00009,0.00006,0.00011,0.00006,0.00012,0.00012,0.00012,0.00012,0.00011,0.00011,0.00014,0.00011,0.00011,0.00011,0.00014,0.00006,0.00011,0.00009,0.00011,0.00009,0.00015,0.00015,0.00015,0.00009,0.00018,0.00015,0.00015,0.00015,0.00017,0.00018,0.00018,0.00015,0.00018,0.00020,0.00024,0.00021,0.00023,0.00027,0.00024,0.00024,0.00027,0.00023,0.00020,0.00029,0.00020,0.00027,0.00020,0.00027,0.00026,0.00034,0.00024,0.00034,0.00031,0.00037,0.00043,0.00038,0.00038,0.00035,0.00047,0.00056,0.00058,0.00041,0.00047,0.00056,0.00072,0.00044,0.00060,0.00072,0.00061,0.00072,0.00066,0.00085,0.00075,0.00078,0.00082,0.00073,0.00108,0.00089,0.00105,0.00105,0.00151,0.00150,0.00110,0.00145,0.00163,0.00160,0.00165,0.00232,0.00201,0.00371,0.00365,0.00383,0.00459,0.00583,0.00662,0.00984,0.00969,0.01080,0.01379,0.02063,0.04308,0.05960,0.15816
+decode_histogram(histogram,hist_type)	0.00047,0.00198,0.00601,0.00008,0.00008,0.00005,0.00011,0.00006,0.00009,0.00008,0.00006,0.00009,0.00008,0.00009,0.00008,0.00009,0.00006,0.00006,0.00008,0.00008,0.00008,0.00011,0.00009,0.00008,0.00009,0.00006,0.00011,0.00006,0.00012,0.00012,0.00012,0.00012,0.00011,0.00011,0.00014,0.00011,0.00011,0.00011,0.00014,0.00006,0.00011,0.00009,0.00011,0.00009,0.00015,0.00015,0.00015,0.00009,0.00018,0.00015,0.00015,0.00015,0.00017,0.00018,0.00018,0.00015,0.00018,0.00020,0.00024,0.00021,0.00023,0.00027,0.00024,0.00024,0.00027,0.00023,0.00020,0.00029,0.00020,0.00027,0.00020,0.00027,0.00026,0.00034,0.00024,0.00034,0.00031,0.00037,0.00043,0.00038,0.00038,0.00035,0.00047,0.00056,0.00058,0.00041,0.00047,0.00056,0.00072,0.00044,0.00060,0.00072,0.00061,0.00072,0.00066,0.00085,0.00075,0.00078,0.00082,0.00073,0.00108,0.00089,0.00105,0.00105,0.00151,0.00150,0.00110,0.00145,0.00163,0.00160,0.00165,0.00232,0.00201,0.00371,0.00365,0.00383,0.00459,0.00583,0.00662,0.00984,0.00969,0.01080,0.01379,0.02063,0.04308,0.05960,0.15816,0.59464
 set histogram_type=default;
 set histogram_size=default;
 use test;

sql/item_strfunc.cc

@@ -513,11 +513,10 @@ String *Item_func_decode_histogram::val_str(String *str)
   double prev= 0.0;
   uint i;
   str->length(0);
-  bool first= true;
+  char numbuf[32];
   const uchar *p= (uchar*)res->c_ptr();
   for (i= 0; i < res->length(); i++)
   {
-    char numbuf[32];
     double val;
     switch (type)
     {
@@ -535,13 +534,14 @@ String *Item_func_decode_histogram::val_str(String *str)
     /* show delta with previous value */
     int size= my_snprintf(numbuf, sizeof(numbuf),
                           representation_by_type[type], val - prev);
-    if (first)
-      first= false;
-    else
-      str->append(",");
     str->append(numbuf, size);
+    str->append(",");
     prev= val;
   }
+  /* show delta with max */
+  int size= my_snprintf(numbuf, sizeof(numbuf),
+                        representation_by_type[type], 1.0 - prev);
+  str->append(numbuf, size);
 
   null_value=0;
   return str;