MDEV-15926 MEDIUMINT returns wrong I_S attributes

Problem:

The logic in store_column_type() with a switch on field type was
hard to follow. The part for MEDIUMINT (MYSQL_TYPE_INT24) was not correct.
It erroneously calculated the precision of MEDIUMINT UNSIGNED
as 7 instead of 8.

A similar hard-to-follow switch doing some type specific calculations
resided in adjust_max_effective_column_length(). It was also wrong for
MEDIUMINT (reported as a separate issue in MDEV-15946).

Solution:

1. Introducing a new class Information_schema_numeric_attributes
2. Adding a new virtual method Field::information_schema_numeric_attributes()
3. Splitting the logic in store_column_type() into virtual
   implementations of information_schema_numeric_attributes().
4. In order to avoid adding duplicate code for the integer data types,
   adding a new virtual method Field_int::numeric_precision(),
   which returns the number of digits.

Additional changes:

1. Adding the "const" qualifier to Field::max_display_length()

2. Moving the code from adjust_max_effective_column_length()
  directly to Field::max_display_length().
  There was no any sense to have two implementations:
  - a set of wrong virtual implementations for Field_xxx::max_display_length()
  - additional code in adjust_max_effective_column_length() fixing
    bad results of Field_xxx::max_display_length()
  This change is safe:
  - The code using Field::max_display_length()
    in field.cc, sql_show.cc, sql_type.cc is not affected.
  - The code in rpl_utility.cc is also not affected.
    See a new DBUG_ASSSERT and new comments explaining why.

  In the new reduction, Field_xxx::max_display_length() returns
  correct results for all integer types (except MEDIUMINT, see below).

  Putting implementations of numeric_precision() and max_display_length()
  near each other in field.h made the logic much clearer and thus
  helped to reveal bad results for Field_medium::max_display_length(),
  which returns 9 instead of 8 for signed MEDIUMINT fields.
  This problem will be addressed separately (MDEV-15946).

Note, this change is also useful for pluggable data types (see MDEV-4912),
as now a user defined Field_xxx has a way to control what's returned
in INFORMATION_SCHEMA.COLUMNS.NUMERIC_PRECISION and
INFORMATION_SCHEMA.COLUMNS.NUMERIC_SCALE by implementing
a desired behavior in Field_xxx::information_schema_numeric_attributes().

mysql-test/main/type_int.result

@@ -93,3 +93,18 @@ DROP TABLE t1;
 #
 # End of 10.2 tests
 #
+#
+# Start of 10.3 tests
+#
+#
+# MDEV-15926 MEDIUMINT returns wrong I_S attributes
+#
+CREATE TABLE t1 (a MEDIUMINT, b MEDIUMINT UNSIGNED);
+SELECT COLUMN_NAME, NUMERIC_PRECISION FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA='test' AND TABLE_NAME='t1' ORDER BY COLUMN_NAME;
+COLUMN_NAME	NUMERIC_PRECISION
+a	7
+b	8
+DROP TABLE t1;
+#
+# End of 10.3 tests
+#

mysql-test/main/type_int.test

@@ -76,3 +76,20 @@ DROP TABLE t1;
 --echo #
 --echo # End of 10.2 tests
 --echo #
+
+--echo #
+--echo # Start of 10.3 tests
+--echo #
+
+--echo #
+--echo # MDEV-15926 MEDIUMINT returns wrong I_S attributes
+--echo #
+
+CREATE TABLE t1 (a MEDIUMINT, b MEDIUMINT UNSIGNED);
+SELECT COLUMN_NAME, NUMERIC_PRECISION FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA='test' AND TABLE_NAME='t1' ORDER BY COLUMN_NAME;
+DROP TABLE t1;
+
+
+--echo #
+--echo # End of 10.3 tests
+--echo #

mysql-test/suite/funcs_1/r/is_columns_innodb.result

@@ -427,9 +427,9 @@ def	test	tb1	f19	19	NULL	YES	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) u
 def	test	tb1	f2	2	NULL	YES	char	0	0	NULL	NULL	NULL	latin1	latin1_bin	char(0)			select,insert,update,references		NEVER	NULL
 def	test	tb1	f20	20	NULL	YES	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb1	f21	21	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(9)			select,insert,update,references		NEVER	NULL
-def	test	tb1	f22	22	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
-def	test	tb1	f23	23	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
-def	test	tb1	f24	24	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb1	f22	22	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
+def	test	tb1	f23	23	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb1	f24	24	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb1	f25	25	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11)			select,insert,update,references		NEVER	NULL
 def	test	tb1	f26	26	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned			select,insert,update,references		NEVER	NULL
 def	test	tb1	f27	27	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned zerofill			select,insert,update,references		NEVER	NULL
@@ -543,9 +543,9 @@ def	test	tb3	f135	18	999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) un
 def	test	tb3	f136	19	00999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f137	20	00999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f138	21	9999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(9)			select,insert,update,references		NEVER	NULL
-def	test	tb3	f139	22	9999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
-def	test	tb3	f140	23	00009999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
-def	test	tb3	f141	24	00009999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb3	f139	22	9999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
+def	test	tb3	f140	23	00009999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb3	f141	24	00009999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f142	25	99999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11)			select,insert,update,references		NEVER	NULL
 def	test	tb3	f143	26	99999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned			select,insert,update,references		NEVER	NULL
 def	test	tb3	f144	27	0000099999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned zerofill			select,insert,update,references		NEVER	NULL

mysql-test/suite/funcs_1/r/is_columns_memory.result

@@ -434,9 +434,9 @@ def	test	tb1	f19	11	NULL	YES	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) u
 def	test	tb1	f2	2	NULL	YES	char	1	1	NULL	NULL	NULL	latin1	latin1_bin	char(1)			select,insert,update,references		NEVER	NULL
 def	test	tb1	f20	12	NULL	YES	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb1	f21	13	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(9)			select,insert,update,references		NEVER	NULL
-def	test	tb1	f22	14	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
-def	test	tb1	f23	15	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
-def	test	tb1	f24	16	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb1	f22	14	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
+def	test	tb1	f23	15	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb1	f24	16	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb1	f25	17	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11)			select,insert,update,references		NEVER	NULL
 def	test	tb1	f26	18	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned			select,insert,update,references		NEVER	NULL
 def	test	tb1	f27	19	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned zerofill			select,insert,update,references		NEVER	NULL
@@ -538,9 +538,9 @@ def	test	tb3	f135	12	999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) un
 def	test	tb3	f136	13	00999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f137	14	00999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f138	15	9999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(9)			select,insert,update,references		NEVER	NULL
-def	test	tb3	f139	16	9999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
-def	test	tb3	f140	17	00009999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
-def	test	tb3	f141	18	00009999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb3	f139	16	9999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
+def	test	tb3	f140	17	00009999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb3	f141	18	00009999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f142	19	99999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11)			select,insert,update,references		NEVER	NULL
 def	test	tb3	f143	20	99999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned			select,insert,update,references		NEVER	NULL
 def	test	tb3	f144	21	0000099999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned zerofill			select,insert,update,references		NEVER	NULL

mysql-test/suite/funcs_1/r/is_columns_myisam.result

@@ -476,9 +476,9 @@ def	test	tb1	f19	19	NULL	YES	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) u
 def	test	tb1	f2	2	NULL	YES	char	1	1	NULL	NULL	NULL	latin1	latin1_bin	char(1)			select,insert,update,references		NEVER	NULL
 def	test	tb1	f20	20	NULL	YES	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb1	f21	21	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(9)			select,insert,update,references		NEVER	NULL
-def	test	tb1	f22	22	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
-def	test	tb1	f23	23	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
-def	test	tb1	f24	24	NULL	YES	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb1	f22	22	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
+def	test	tb1	f23	23	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb1	f24	24	NULL	YES	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb1	f25	25	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11)			select,insert,update,references		NEVER	NULL
 def	test	tb1	f26	26	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned			select,insert,update,references		NEVER	NULL
 def	test	tb1	f27	27	NULL	YES	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned zerofill			select,insert,update,references		NEVER	NULL
@@ -600,9 +600,9 @@ def	test	tb3	f135	18	999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) un
 def	test	tb3	f136	19	00999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f137	20	00999	NO	smallint	NULL	NULL	5	0	NULL	NULL	NULL	smallint(5) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f138	21	9999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(9)			select,insert,update,references		NEVER	NULL
-def	test	tb3	f139	22	9999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
-def	test	tb3	f140	23	00009999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
-def	test	tb3	f141	24	00009999	NO	mediumint	NULL	NULL	7	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb3	f139	22	9999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned			select,insert,update,references		NEVER	NULL
+def	test	tb3	f140	23	00009999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
+def	test	tb3	f141	24	00009999	NO	mediumint	NULL	NULL	8	0	NULL	NULL	NULL	mediumint(8) unsigned zerofill			select,insert,update,references		NEVER	NULL
 def	test	tb3	f142	25	99999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11)			select,insert,update,references		NEVER	NULL
 def	test	tb3	f143	26	99999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned			select,insert,update,references		NEVER	NULL
 def	test	tb3	f144	27	0000099999	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(10) unsigned zerofill			select,insert,update,references		NEVER	NULL

sql/field.cc

@@ -11072,7 +11072,7 @@ bool Column_definition::set_compressed(const char *method)
     length
 */
 
-uint32 Field_blob::max_display_length()
+uint32 Field_blob::max_display_length() const
 {
   switch (packlength)
   {

sql/item.cc

@@ -3187,33 +3187,6 @@ inline static uint32
 adjust_max_effective_column_length(Field *field_par, uint32 max_length)
 {
   uint32 new_max_length= field_par->max_display_length();
-  uint32 sign_length= (field_par->flags & UNSIGNED_FLAG) ? 0 : 1;
-
-  switch (field_par->type())
-  {
-  case MYSQL_TYPE_INT24:
-    /*
-      Compensate for MAX_MEDIUMINT_WIDTH being 1 too long (8)
-      compared to the actual number of digits that can fit into
-      the column.
-    */
-    new_max_length+= 1;
-    /* fall through */
-  case MYSQL_TYPE_LONG:
-  case MYSQL_TYPE_TINY:
-  case MYSQL_TYPE_SHORT:
-
-    /* Take out the sign and add a conditional sign */
-    new_max_length= new_max_length - 1 + sign_length;
-    break;
-
-  /* BINGINT is always 20 no matter the sign */
-  case MYSQL_TYPE_LONGLONG:
-  /* make gcc happy */
-  default:
-    break;
-  }
-
   /* Adjust only if the actual precision based one is bigger than specified */
   return new_max_length > max_length ? new_max_length : max_length;
 }

sql/rpl_utility.cc

@@ -42,6 +42,12 @@ max_display_length_for_temporal2_field(uint32 int_display_length,
    @param sql_type Type of the field
    @param metadata The metadata from the master for the field.
    @return Maximum length of the field in bytes.
+
+   The precise values calculated by field->max_display_length() and
+   calculated by max_display_length_for_field() can differ (by +1 or -1)
+   for integer data types (TINYINT, SMALLINT, MEDIUMINT, INT, BIGINT).
+   This slight difference is not important here, because we call
+   this function only for two *different* integer data types.
  */
 static uint32
 max_display_length_for_field(enum_field_types sql_type, unsigned int metadata)
@@ -737,6 +743,16 @@ can_convert_field_to(Field *field,
     case MYSQL_TYPE_INT24:
     case MYSQL_TYPE_LONG:
     case MYSQL_TYPE_LONGLONG:
+      /*
+        max_display_length_for_field() is not fully precise for the integer
+        data types. So its result cannot be compared to the result of
+        field->max_dispay_length() when the table field and the binlog field
+        are of the same type.
+        This code should eventually be rewritten not to use
+        compare_lengths(), to detect subtype/supetype relations
+        just using the type codes.
+      */
+      DBUG_ASSERT(source_type != field->real_type());
       *order_var= compare_lengths(field, source_type, metadata);
       DBUG_ASSERT(*order_var != 0);
       DBUG_RETURN(is_conversion_ok(*order_var, rli));

sql/sql_show.cc

@@ -5636,7 +5636,6 @@ static void store_column_type(TABLE *table, Field *field, CHARSET_INFO *cs,
                               uint offset)
 {
   bool is_blob;
-  int decimals, field_length;
   const char *tmp_buff;
   char column_type_buff[MAX_FIELD_WIDTH];
   String column_type(column_type_buff, sizeof(column_type_buff), cs);
@@ -5686,35 +5685,10 @@ static void store_column_type(TABLE *table, Field *field, CHARSET_INFO *cs,
     They are set to -1 if they should not be set (we should return NULL)
   */
 
-  field_length= -1;
-  decimals= field->decimals();
+  Information_schema_numeric_attributes num=
+    field->information_schema_numeric_attributes();
+
   switch (field->type()) {
-  case MYSQL_TYPE_NEWDECIMAL:
-    field_length= ((Field_new_decimal*) field)->precision;
-    break;
-  case MYSQL_TYPE_DECIMAL:
-    field_length= field->field_length - (decimals  ? 2 : 1);
-    break;
-  case MYSQL_TYPE_TINY:
-  case MYSQL_TYPE_SHORT:
-  case MYSQL_TYPE_LONG:
-  case MYSQL_TYPE_INT24:
-    field_length= field->max_display_length() - 1;
-    break;
-  case MYSQL_TYPE_LONGLONG:
-    field_length= field->max_display_length() - 
-      ((field->flags & UNSIGNED_FLAG) ? 0 : 1);
-    break;
-  case MYSQL_TYPE_BIT:
-    field_length= field->max_display_length();
-    decimals= -1;                             // return NULL
-    break;
-  case MYSQL_TYPE_FLOAT:  
-  case MYSQL_TYPE_DOUBLE:
-    field_length= field->field_length;
-    if (decimals == NOT_FIXED_DEC)
-      decimals= -1;                           // return NULL
-    break;
   case MYSQL_TYPE_TIME:
   case MYSQL_TYPE_TIMESTAMP:
   case MYSQL_TYPE_DATETIME:
@@ -5727,15 +5701,15 @@ static void store_column_type(TABLE *table, Field *field, CHARSET_INFO *cs,
   }
 
   /* NUMERIC_PRECISION column */
-  if (field_length >= 0)
+  if (num.has_precision())
   {
-    table->field[offset + 3]->store((longlong) field_length, TRUE);
+    table->field[offset + 3]->store((longlong) num.precision(), true);
     table->field[offset + 3]->set_notnull();
 
     /* NUMERIC_SCALE column */
-    if (decimals >= 0)
+    if (num.has_scale())
     {
-      table->field[offset + 4]->store((longlong) decimals, TRUE);
+      table->field[offset + 4]->store((longlong) num.scale(), true);
       table->field[offset + 4]->set_notnull();
     }
   }

sql/sql_type.h

@@ -911,6 +911,46 @@ class Record_addr
 };
 
 
+class Information_schema_numeric_attributes
+{
+  enum enum_attr
+  {
+    ATTR_NONE= 0,
+    ATTR_PRECISION= 1,
+    ATTR_SCALE= 2,
+    ATTR_PRECISION_AND_SCALE= (ATTR_PRECISION|ATTR_SCALE)
+  };
+  uint m_precision;
+  uint m_scale;
+  enum_attr m_available_attributes;
+public:
+  Information_schema_numeric_attributes()
+   :m_precision(0), m_scale(0),
+    m_available_attributes(ATTR_NONE)
+  { }
+  Information_schema_numeric_attributes(uint precision)
+   :m_precision(precision), m_scale(0),
+    m_available_attributes(ATTR_PRECISION)
+  { }
+  Information_schema_numeric_attributes(uint precision, uint scale)
+   :m_precision(precision), m_scale(scale),
+    m_available_attributes(ATTR_PRECISION_AND_SCALE)
+  { }
+  bool has_precision() const { return m_available_attributes & ATTR_PRECISION; }
+  bool has_scale() const { return m_available_attributes & ATTR_SCALE; }
+  uint precision() const
+  {
+    DBUG_ASSERT(has_precision());
+    return (uint) m_precision;
+  }
+  uint scale() const
+  {
+    DBUG_ASSERT(has_scale());
+    return (uint) m_scale;
+  }
+};
+
+
 class Type_handler
 {
 protected: