fix: find the right wider decimal datatype for comparison operation

[liukun4515]

Which issue does this PR close?

Closes #2232

For decimal with the comparison operation, we use the error algorithm to calculate the precision/scale.

Before: max(p1,p2),max(s1,s2)

Now: max(38,max(s1, s2) + max(p1-s1, p2-s2)), max(s1, s2, 38)

Rationale for this change

What changes are included in this PR?

schema

CREATE EXTERNAL TABLE food (a DECIMAL(10,6), b double, c boolean) STORED AS CSV LOCATION 'aggregate_simple.csv';

Before this fix, we got the plan #2200 (comment)

After this fix, we got the right converted type in the filter expr

❯ explain select * from food where a >= CAST(0.00002 as Decimal(10,8));
+---------------+----------------------------------------------------------------------------------------------------------+
| plan_type     | plan                                                                                                     |
+---------------+----------------------------------------------------------------------------------------------------------+
| logical_plan  | Projection: #food.a, #food.b, #food.c                                                                    |
|               |   Filter: #food.a >= Decimal128(Some(2000),10,8)                                                         |
|               |     TableScan: food projection=Some([0, 1, 2]), partial_filters=[#food.a >= Decimal128(Some(2000),10,8)] |
| physical_plan | ProjectionExec: expr=[a@0 as a, b@1 as b, c@2 as c]                                                      |
|               |   CoalesceBatchesExec: target_batch_size=4096                                                            |
|               |     FilterExec: CAST(a@0 AS Decimal(12, 8)) >= CAST(Some(2000),10,8 AS Decimal(12, 8))                   |
|               |       RepartitionExec: partitioning=RoundRobinBatch(16)                                                  |
|               |         CsvExec: files=[aggregate_simple.csv], has_header=false, limit=None, projection=[a, b, c]        |
|               |                                                                                                          |
+---------------+----------------------------------------------------------------------------------------------------------+

Are there any user-facing changes?

cc @alamb

[alamb]

Thanks @liukun4515

[alamb]

👍 I see that the precision includes the scale 👍

[alamb]

👍

[liukun4515]

This is inspired by your comments #2200 (comment)
Thanks