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().

1 files changed, 0 insertions, 27 deletions

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;
 }