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, 24 insertions, 0 deletions

diff --git a/mysql-test/t/type_float.test b/mysql-test/t/type_float.test
index ec0256beeef..f54eacf0595 100644
--- a/mysql-test/t/type_float.test
+++ b/mysql-test/t/type_float.test
@@ -510,5 +510,29 @@ SELECT * FROM t1;
 DROP TABLE t1,t2;
 
 --echo #
+--echo # Test of using wrong scale
+--echo #
+
+create or replace table t1 (a double(40,30));
+--error ER_TOO_BIG_SCALE 1425
+create or replace table t1 (a double(40,31));
+create or replace table t1 as select 1.01e1;
+show create table t1;
+create or replace table t1 as select truncate(10.000000000001e1, 30) as t;
+show create table t1;
+create or replace table t1 as select truncate(10.000000000001e1, 31) as t;
+show create table t1;
+create or replace table t1 as select truncate(10.000000000001e1, 39) as t;
+show create table t1;
+create or replace table t1 as select truncate(10.000000000001e1, 51) as t;
+show create table t1;
+create or replace table t1 as select truncate(10.000000000001e1, 20)/2 as t;
+show create table t1;
+create or replace table t1 as select truncate(10.000000000001e1, 28)/2 as t;
+show create table t1;
+
+drop table if exists t1;
+
+--echo #
 --echo # End of 10.2 tests
 --echo #