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().

11 files changed, 224 insertions, 95 deletions

diff --git a/mysql-test/main/type_int.result b/mysql-test/main/type_int.result
index 39e2e91ecc7..bd24641fd65 100644
--- a/mysql-test/main/type_int.result
+++ b/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
+#
diff --git a/mysql-test/main/type_int.test b/mysql-test/main/type_int.test
index 271b4d5862a..f0df08ffa2c 100644
--- a/mysql-test/main/type_int.test
+++ b/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 #
diff --git a/mysql-test/suite/funcs_1/r/is_columns_innodb.result b/mysql-test/suite/funcs_1/r/is_columns_innodb.result
index 297dc2d33f8..8f2ba33b591 100644
--- a/mysql-test/suite/funcs_1/r/is_columns_innodb.result
+++ b/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
diff --git a/mysql-test/suite/funcs_1/r/is_columns_memory.result b/mysql-test/suite/funcs_1/r/is_columns_memory.result
index e94d4c9123a..5eaa5b08cc2 100644
--- a/mysql-test/suite/funcs_1/r/is_columns_memory.result
+++ b/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
diff --git a/mysql-test/suite/funcs_1/r/is_columns_myisam.result b/mysql-test/suite/funcs_1/r/is_columns_myisam.result
index c4e11e3f48b..4426583ac4c 100644
--- a/mysql-test/suite/funcs_1/r/is_columns_myisam.result
+++ b/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
diff --git a/sql/field.cc b/sql/field.cc
index 58b8105c00f..fceb3cc17d7 100644
--- a/sql/field.cc
+++ b/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)
   {
diff --git a/sql/field.h b/sql/field.h
index 7bd79630265..cdb62d6af16 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -1116,6 +1116,11 @@ public:
      memcpy(ptr, val, len);
   }
   virtual uint decimals() const { return 0; }
+  virtual Information_schema_numeric_attributes
+            information_schema_numeric_attributes() const
+  {
+    return Information_schema_numeric_attributes();
+  }
   /*
     Caller beware: sql_type can change str.Ptr, so check
     ptr() to see if it changed if you are using your own buffer
@@ -1390,8 +1395,7 @@ public:
   }
 
   /* maximum possible display length */
-  virtual uint32 max_display_length()= 0;
-
+  virtual uint32 max_display_length() const= 0;
   /**
     Whether a field being created is compatible with a existing one.
 
@@ -1726,7 +1730,7 @@ public:
   CHARSET_INFO *charset(void) const { return field_charset; }
   enum Derivation derivation(void) const { return field_derivation; }
   bool binary() const { return field_charset == &my_charset_bin; }
-  uint32 max_display_length() { return field_length; }
+  uint32 max_display_length() const { return field_length; }
   friend class Create_field;
   my_decimal *val_decimal(my_decimal *);
   bool val_bool() { return val_real() != 0e0; }
@@ -1817,6 +1821,13 @@ public:
   {
     return do_field_real;
   }
+  Information_schema_numeric_attributes
+    information_schema_numeric_attributes() const
+  {
+    return dec == NOT_FIXED_DEC ?
+                  Information_schema_numeric_attributes(field_length) :
+                  Information_schema_numeric_attributes(field_length, dec);
+  }
   int save_in_field(Field *to) { return to->store(val_real()); }
   bool memcpy_field_possible(const Field *from) const
   {
@@ -1833,7 +1844,7 @@ public:
   bool get_date(MYSQL_TIME *ltime, ulonglong fuzzydate);
   my_decimal *val_decimal(my_decimal *);
   bool val_bool() { return val_real() != 0e0; }
-  uint32 max_display_length() { return field_length; }
+  uint32 max_display_length() const { return field_length; }
   uint size_of() const { return sizeof(*this); }
   Item *get_equal_const_item(THD *thd, const Context &ctx, Item *const_item);
 };
@@ -1852,6 +1863,12 @@ public:
   const Type_handler *type_handler() const { return &type_handler_olddecimal; }
   enum ha_base_keytype key_type() const
   { return zerofill ? HA_KEYTYPE_BINARY : HA_KEYTYPE_NUM; }
+  Information_schema_numeric_attributes
+    information_schema_numeric_attributes() const
+  {
+    uint tmp= dec ? 2 : 1; // The sign and the decimal point
+    return Information_schema_numeric_attributes(field_length - tmp, dec);
+  }
   Copy_func *get_copy_func(const Field *from) const
   {
     return eq_def(from) ? get_identical_copy_func() : do_field_string;
@@ -1936,7 +1953,12 @@ public:
   void sort_string(uchar *buff, uint length);
   bool zero_pack() const { return 0; }
   void sql_type(String &str) const;
-  uint32 max_display_length() { return field_length; }
+  uint32 max_display_length() const { return field_length; }
+  Information_schema_numeric_attributes
+    information_schema_numeric_attributes() const
+  {
+    return Information_schema_numeric_attributes(precision, dec);
+  }
   uint size_of() const { return sizeof(*this); } 
   uint32 pack_length() const { return (uint32) bin_size; }
   uint pack_length_from_metadata(uint field_metadata);
@@ -1954,6 +1976,7 @@ class Field_int :public Field_num
 protected:
   String *val_str_from_long(String *val_buffer, uint max_char_length,
                             int radix, long nr);
+  uint32 sign_length() const { return (flags & UNSIGNED_FLAG) ? 0 : 1; }
 public:
   Field_int(uchar *ptr_arg, uint32 len_arg, uchar *null_ptr_arg,
             uchar null_bit_arg, enum utype unireg_check_arg,
@@ -1966,6 +1989,12 @@ public:
   bool val_bool() { return val_int() != 0; }
   int  store_time_dec(const MYSQL_TIME *ltime, uint dec);
   bool get_date(MYSQL_TIME *ltime, ulonglong fuzzydate);
+  virtual uint numeric_precision() const= 0;
+  Information_schema_numeric_attributes
+    information_schema_numeric_attributes() const
+  {
+    return Information_schema_numeric_attributes(numeric_precision(), 0);
+  }
 };
 
 
@@ -1994,7 +2023,18 @@ public:
   void sort_string(uchar *buff,uint length);
   uint32 pack_length() const { return 1; }
   void sql_type(String &str) const;
-  uint32 max_display_length() { return 4; }
+  /*
+     SIGNED: -128..127  digits=3 nchars=4
+     UNDIGNED: 0..255   digits=3 nchars=3
+  */
+  uint numeric_precision() const
+  {
+    return MAX_TINYINT_WIDTH;
+  }
+  uint32 max_display_length() const
+  {
+    return MAX_TINYINT_WIDTH + sign_length();
+  }
 
   virtual uchar *pack(uchar* to, const uchar *from, uint max_length)
   {
@@ -2044,7 +2084,18 @@ public:
   void sort_string(uchar *buff,uint length);
   uint32 pack_length() const { return 2; }
   void sql_type(String &str) const;
-  uint32 max_display_length() { return 6; }
+  /*
+    SIGNED:   -32768..32767  digits=5 nchars=6
+    UNDIGNED:      0..65535  digits=5 nchars=5
+  */
+  uint numeric_precision() const
+  {
+    return MAX_SMALLINT_WIDTH;
+  }
+  uint32 max_display_length() const
+  {
+    return MAX_SMALLINT_WIDTH + sign_length();
+  }
 
   virtual uchar *pack(uchar* to, const uchar *from, uint max_length)
   { return pack_int16(to, from); }
@@ -2079,7 +2130,21 @@ public:
   void sort_string(uchar *buff,uint length);
   uint32 pack_length() const { return 3; }
   void sql_type(String &str) const;
-  uint32 max_display_length() { return 8; }
+  /*
+    MEDIUMINT has a different number of digits for signed and unsigned:
+    MEDIUMINT SIGNED:   -8388608 ..  8388607  digits=7 char_length=8
+    MEDIUMINT UNSIGNED         0 .. 16777215  digits=8 char_length=8
+  */
+  uint numeric_precision() const
+  {
+    uint ndigits= MAX_MEDIUMINT_WIDTH - 1 + MY_TEST(flags & UNSIGNED_FLAG);
+    return ndigits;
+  }
+  uint32 max_display_length() const
+  {
+    // Looks too long for SIGNED: See MDEV-15946
+    return MAX_MEDIUMINT_WIDTH + sign_length();
+  }
 
   virtual uchar *pack(uchar* to, const uchar *from, uint max_length)
   {
@@ -2119,7 +2184,18 @@ public:
   void sort_string(uchar *buff,uint length);
   uint32 pack_length() const { return 4; }
   void sql_type(String &str) const;
-  uint32 max_display_length() { return MY_INT32_NUM_DECIMAL_DIGITS; }
+  /*
+    SIGNED:   -2147483648..2147483647  digits=10 nchars=11
+    UNSIGNED:           0..4294967295  digits=10 nchars=10
+  */
+  uint numeric_precision() const
+  {
+    return MAX_INT_WIDTH;
+  }
+  uint32 max_display_length() const
+  {
+    return MAX_INT_WIDTH + sign_length();
+  }
   virtual uchar *pack(uchar* to, const uchar *from,
                       uint max_length __attribute__((unused)))
   {
@@ -2169,7 +2245,15 @@ public:
   void sort_string(uchar *buff,uint length);
   uint32 pack_length() const { return 8; }
   void sql_type(String &str) const;
-  uint32 max_display_length() { return 20; }
+  /*
+    SIGNED:  -9223372036854775808..9223372036854775807 digits=19 nchars=20
+    UNSIGNED:                  0..18446744073709551615 digits=20 nchars=20
+  */
+  uint numeric_precision() const
+  {
+    return MAX_BIGINT_WIDTH - sign_length();
+  }
+  uint32 max_display_length() const { return MAX_BIGINT_WIDTH; }
   virtual uchar *pack(uchar* to, const uchar *from,
                       uint max_length  __attribute__((unused)))
   {
@@ -2361,7 +2445,7 @@ public:
   uint32 pack_length() const { return 0; }
   void sql_type(String &str) const;
   uint size_of() const { return sizeof(*this); }
-  uint32 max_display_length() { return 4; }
+  uint32 max_display_length() const { return 4; }
   void move_field_offset(my_ptrdiff_t ptr_diff) {}
   bool can_optimize_keypart_ref(const Item_bool_func *cond,
                                 const Item *item) const
@@ -2400,7 +2484,7 @@ public:
     return to->store_time_dec(&ltime, decimals());
   }
   bool memcpy_field_possible(const Field *from) const;
-  uint32 max_display_length() { return field_length; }
+  uint32 max_display_length() const { return field_length; }
   bool str_needs_quotes() { return TRUE; }
   enum Derivation derivation(void) const { return DERIVATION_NUMERIC; }
   uint repertoire(void) const { return MY_REPERTOIRE_NUMERIC; }
@@ -2700,7 +2784,12 @@ public:
   String *val_str(String*,String *);
   bool get_date(MYSQL_TIME *ltime, ulonglong fuzzydate);
   bool send_binary(Protocol *protocol);
-  uint32 max_display_length() { return field_length; }
+  Information_schema_numeric_attributes
+    information_schema_numeric_attributes() const
+  {
+    return Information_schema_numeric_attributes();
+  }
+  uint32 max_display_length() const { return field_length; }
   void sql_type(String &str) const;
 };
 
@@ -3355,7 +3444,7 @@ private:
     Field_varstring::sql_type(str);
     str.append(STRING_WITH_LEN(" /*!100301 COMPRESSED*/"));
   }
-  uint32 max_display_length() { return field_length - 1; }
+  uint32 max_display_length() const { return field_length - 1; }
   int cmp_max(const uchar *a_ptr, const uchar *b_ptr, uint max_len);
 
   /*
@@ -3635,7 +3724,7 @@ public:
   uint size_of() const { return sizeof(*this); }
   bool has_charset(void) const
   { return charset() == &my_charset_bin ? FALSE : TRUE; }
-  uint32 max_display_length();
+  uint32 max_display_length() const;
   uint32 char_length() const;
   uint is_equal(Create_field *new_field);
 private:
@@ -3915,7 +4004,12 @@ public:
   enum ha_base_keytype key_type() const { return HA_KEYTYPE_BIT; }
   uint32 key_length() const { return (uint32) (field_length + 7) / 8; }
   uint32 max_data_length() const { return (field_length + 7) / 8; }
-  uint32 max_display_length() { return field_length; }
+  uint32 max_display_length() const { return field_length; }
+  Information_schema_numeric_attributes
+    information_schema_numeric_attributes() const
+  {
+    return Information_schema_numeric_attributes(field_length);
+  }
   uint size_of() const { return sizeof(*this); }
   int reset(void) { 
     bzero(ptr, bytes_in_rec); 
diff --git a/sql/item.cc b/sql/item.cc
index 56af69be427..35c5ab8cc3d 100644
--- a/sql/item.cc
+++ b/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;
 }
diff --git a/sql/rpl_utility.cc b/sql/rpl_utility.cc
index 58711078db6..31035fb5dcc 100644
--- a/sql/rpl_utility.cc
+++ b/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));
diff --git a/sql/sql_show.cc b/sql/sql_show.cc
index 38a13c49278..a45ca325d1a 100644
--- a/sql/sql_show.cc
+++ b/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();
     }
   }
diff --git a/sql/sql_type.h b/sql/sql_type.h
index dd37e2ba96c..e9307db7125 100644
--- a/sql/sql_type.h
+++ b/sql/sql_type.h
@@ -911,6 +911,46 @@ public:
 };
 
 
+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: