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, 5 insertions, 3 deletions

diff --git a/sql/item_sum.cc b/sql/item_sum.cc
index f774ee5a561..f7e02bc55f9 100644
--- a/sql/item_sum.cc
+++ b/sql/item_sum.cc
@@ -1624,7 +1624,8 @@ void Item_sum_avg::fix_length_and_dec()
   }
   else
   {
-    decimals= MY_MIN(args[0]->decimals + prec_increment, NOT_FIXED_DEC);
+    decimals= MY_MIN(args[0]->decimals + prec_increment,
+                     FLOATING_POINT_DECIMALS);
     max_length= MY_MIN(args[0]->max_length + prec_increment, float_length(decimals));
   }
 }
@@ -1839,13 +1840,14 @@ void Item_sum_variance::fix_length_and_dec()
   switch (args[0]->result_type()) {
   case REAL_RESULT:
   case STRING_RESULT:
-    decimals= MY_MIN(args[0]->decimals + 4, NOT_FIXED_DEC);
+    decimals= MY_MIN(args[0]->decimals + 4, FLOATING_POINT_DECIMALS);
     break;
   case INT_RESULT:
   case DECIMAL_RESULT:
   {
     int precision= args[0]->decimal_precision()*2 + prec_increment;
-    decimals= MY_MIN(args[0]->decimals + prec_increment, DECIMAL_MAX_SCALE);
+    decimals= MY_MIN(args[0]->decimals + prec_increment,
+                     FLOATING_POINT_DECIMALS-1);
     max_length= my_decimal_precision_to_length_no_truncation(precision,
                                                              decimals,
                                                              unsigned_flag);