MDEV-4402 A function to visualize histograms data.

4 files changed, 115 insertions, 2 deletions

diff --git a/sql/item_create.cc b/sql/item_create.cc
index c1cefed6f8b..ce4dc7ced8f 100644
--- a/sql/item_create.cc
+++ b/sql/item_create.cc
@@ -614,6 +614,19 @@ protected:
 };
 
 
+class Create_func_decode_histogram : public Create_func_arg2
+{
+public:
+  Item *create_2_arg(THD *thd, Item *arg1, Item *arg2);
+
+  static Create_func_decode_histogram s_singleton;
+
+protected:
+  Create_func_decode_histogram() {}
+  virtual ~Create_func_decode_histogram() {}
+};
+
+
 class Create_func_concat_ws : public Create_native_func
 {
 public:
@@ -3231,6 +3244,13 @@ Create_func_concat::create_native(THD *thd, LEX_STRING name,
   return new (thd->mem_root) Item_func_concat(*item_list);
 }
 
+Create_func_decode_histogram Create_func_decode_histogram::s_singleton;
+
+Item *
+Create_func_decode_histogram::create_2_arg(THD *thd, Item *arg1, Item *arg2)
+{
+  return new (thd->mem_root) Item_func_decode_histogram(arg1, arg2);
+}
 
 Create_func_concat_ws Create_func_concat_ws::s_singleton;
 
@@ -5377,6 +5397,7 @@ static Native_func_registry func_array[] =
   { { C_STRING_WITH_LEN("DAYOFYEAR") }, BUILDER(Create_func_dayofyear)},
   { { C_STRING_WITH_LEN("DECODE") }, BUILDER(Create_func_decode)},
   { { C_STRING_WITH_LEN("DEGREES") }, BUILDER(Create_func_degrees)},
+  { { C_STRING_WITH_LEN("DECODE_HISTOGRAM") }, BUILDER(Create_func_decode_histogram)},
   { { C_STRING_WITH_LEN("DES_DECRYPT") }, BUILDER(Create_func_des_decrypt)},
   { { C_STRING_WITH_LEN("DES_ENCRYPT") }, BUILDER(Create_func_des_encrypt)},
   { { C_STRING_WITH_LEN("DIMENSION") }, GEOM_BUILDER(Create_func_dimension)},
diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 93569082d74..5cce910758a 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -60,6 +60,7 @@ C_MODE_START
 C_MODE_END
 #include "sql_show.h"                           // append_identifier
 #include <sql_repl.h>
+#include "sql_statistics.h"
 
 /**
    @todo Remove this. It is not safe to use a shared String object.
@@ -472,6 +473,82 @@ void Item_func_aes_decrypt::fix_length_and_dec()
    set_persist_maybe_null(1);
 }
 
+///////////////////////////////////////////////////////////////////////////////
+
+
+const char *histogram_types[] =
+           {"SINGLE_PREC_HB", "DOUBLE_PREC_HB", 0};
+static TYPELIB hystorgam_types_typelib=
+  { array_elements(histogram_types),
+    "histogram_types",
+    histogram_types, NULL};
+const char *representation_by_type[]= {"%.3f", "%.5f"};
+
+String *Item_func_decode_histogram::val_str(String *str)
+{
+  DBUG_ASSERT(fixed == 1);
+  char buff[STRING_BUFFER_USUAL_SIZE];
+  String *res, tmp(buff, sizeof(buff), &my_charset_bin);
+  int type;
+
+  tmp.length(0);
+  if (!(res= args[1]->val_str(&tmp)) ||
+      (type= find_type(res->c_ptr_safe(),
+                       &hystorgam_types_typelib, MYF(0))) <= 0)
+  {
+    null_value= 1;
+    return 0;
+  }
+  type--;
+
+  tmp.length(0);
+  if (!(res= args[0]->val_str(&tmp)))
+  {
+    null_value= 1;
+    return 0;
+  }
+  if (type == DOUBLE_PREC_HB && res->length() % 2 != 0)
+    res->length(res->length() - 1); // one byte is unused
+
+  double prev= 0.0;
+  uint i;
+  str->length(0);
+  bool first= true;
+  const uchar *p= (uchar*)res->c_ptr();
+  for (i= 0; i < res->length(); i++)
+  {
+    char numbuf[32];
+    double val;
+    switch (type)
+    {
+    case SINGLE_PREC_HB:
+      val= p[i] / ((double)((1 << 8) - 1));
+      break;
+    case DOUBLE_PREC_HB:
+      val= ((uint16 *)(p + i))[0] / ((double)((1 << 16) - 1));
+      i++;
+      break;
+    default:
+      val= 0;
+      DBUG_ASSERT(0);
+    }
+    /* 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);
+    prev= val;
+  }
+
+  null_value=0;
+  return str;
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
 
 /**
   Concatenate args with the following premises:
diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
index 89d7fa67f6b..169da25e826 100644
--- a/sql/item_strfunc.h
+++ b/sql/item_strfunc.h
@@ -143,6 +143,22 @@ public:
   const char *func_name() const { return "concat"; }
 };
 
+class Item_func_decode_histogram :public Item_str_func
+{
+  String tmp_value;
+public:
+  Item_func_decode_histogram(Item *a, Item *b)
+    :Item_str_func(a, b) {}
+  String *val_str(String *);
+  void fix_length_and_dec()
+  {
+    collation.set(system_charset_info);
+    max_length= MAX_BLOB_WIDTH;
+    set_persist_maybe_null(1);
+  }
+  const char *func_name() const { return "decode_histogram"; }
+};
+
 class Item_func_concat_ws :public Item_str_func
 {
   String tmp_value;
diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index 24009cb5a99..e51fd1cc11c 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -3970,8 +3970,7 @@ static Sys_var_ulong Sys_histogram_size(
        SESSION_VAR(histogram_size), CMD_LINE(REQUIRED_ARG),
        VALID_RANGE(0, 255), DEFAULT(0), BLOCK_SIZE(1));
 
-const char *histogram_types[] =
-           {"SINGLE_PREC_HB", "DOUBLE_PREC_HB", 0};
+extern const char *histogram_types[];
 static Sys_var_enum Sys_histogram_type(
        "histogram_type",
        "Specifies type of the histograms created by ANALYZE. "