MDEV-10138 Support for decimals up to 38 digits

Decimals with float, double and decimal now works the following way:

- DECIMAL_NOT_SPECIFIED is used when declaring DECIMALS without a firm number
  of decimals.  It's only used in asserts and my_decimal_int_part.
- FLOATING_POINT_DECIMALS (31) is used to mark that a FLOAT or DOUBLE
  was defined without decimals. This is regarded as a floating point value.
- Max decimals allowed for FLOAT and DOUBLE is FLOATING_POINT_DECIMALS-1
- Clients assumes that float and double with decimals >= NOT_FIXED_DEC are
  floating point values (no decimals)
- In the .frm decimals=FLOATING_POINT_DECIMALS are used to define
  floating point for float and double (31, like before)

To ensure compatibility with old clients we do:

- When storing float and double, we change NOT_FIXED_DEC to
  FLOATING_POINT_DECIMALS.
- When creating fields from .frm we change for float and double
  FLOATING_POINT_DEC to NOT_FIXED_DEC
- When sending definition for a float/decimal field without decimals
  to the client as part of a result set we convert NOT_FIXED_DEC to
  FLOATING_POINT_DECIMALS.
- variance() and std() has changed to limit the decimals to
  FLOATING_POINT_DECIMALS -1 to not get the double converted floating point.
  (This was to preserve compatiblity)
- FLOAT and DOUBLE still have 30 as max number of decimals.

Bugs fixed:

variance() printed more decimals than we support for double values.

New behaviour:
- Strings now have 38 decimals instead of 30 when converted to decimal
- CREATE ... SELECT with a decimal with > 30 decimals will create a column
  with a smaller range than before as we are trying to preserve the number of
  decimals.


Other changes
- We are now using the obsolete bit FIELDFLAG_LEFT_FULLSCREEN to specify
  decimals > 31
- NOT_FIXED_DEC is now declared in one place
- For clients, NOT_FIXED_DEC is always 31 (to ensure compatibility).
  On the server NOT_FIXED_DEC is DECIMAL_NOT_SPECIFIED (39)
- AUTO_SEC_PART_DIGITS is taken from DECIMAL_NOT_SPECIFIED
- DOUBLE conversion functions are now using DECIMAL_NOT_SPECIFIED instead of
  NOT_FIXED_DEC

1 files changed, 3 insertions, 3 deletions

diff --git a/sql/sql_analyse.cc b/sql/sql_analyse.cc
index b2bc9fc2e87..91a80c552cb 100644
--- a/sql/sql_analyse.cc
+++ b/sql/sql_analyse.cc
@@ -409,7 +409,7 @@ void field_real::add()
   if (num == 0.0)
     empty++;
 
-  if ((decs = decimals()) == NOT_FIXED_DEC)
+  if ((decs = decimals()) >= FLOATING_POINT_DECIMALS)
   {
     length= sprintf(buff, "%g", num);
     if (rint(num) != num)
@@ -892,7 +892,7 @@ void field_real::get_opt_type(String *answer,
 
   if (!max_notzero_dec_len)
   {
-    int len= (int) max_length - ((item->decimals == NOT_FIXED_DEC) ?
+    int len= (int) max_length - ((item->decimals >= FLOATING_POINT_DECIMALS) ?
 				 0 : (item->decimals + 1));
 
     if (min_arg >= -128 && max_arg <= (min_arg >= 0 ? 255 : 127))
@@ -912,7 +912,7 @@ void field_real::get_opt_type(String *answer,
     if (min_arg >= 0)
       answer->append(STRING_WITH_LEN(" UNSIGNED"));
   }
-  else if (item->decimals == NOT_FIXED_DEC)
+  else if (item->decimals >= FLOATING_POINT_DECIMALS)
   {
     if (min_arg >= -FLT_MAX && max_arg <= FLT_MAX)
       answer->append(STRING_WITH_LEN("FLOAT"));