gengliangwang opened a new pull request, #38379:
URL: https://github.com/apache/spark/pull/38379

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   ### What changes were proposed in this pull request?
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   Avoid reordering Add for canonicalizing if it is decimal type.
   Expressions are canonicalized for comparisons and explanations. For 
non-decimal Add expression, the order can be sorted by hashcode, and the result 
is supposed to be the same.
   However, for Add expression of Decimal type, the behavior is different: 
Given decimal (p1, s1) and another decimal (p2, s2), the result integral part 
is `max(p1-s1, p2-s2) +1`, the result decimal part is `max(s1, s2)`. Thus the 
result data type is `(max(p1-s1, p2-s2) +1 + max(s1, s2), max(s1, s2))`.
   Thus the order matters:
   
   For `(decimal(12,5) + decimal(12,6)) + decimal(3, 2)`, the first add 
`decimal(12,5) + decimal(12,6)` results in `decimal(14, 6)`, and then 
`decimal(14, 6) + decimal(3, 2)`  results in `decimal(15, 6)`
   For `(decimal(12, 6) + decimal(3,2)) + decimal(12, 5)`, the first add 
`decimal(12, 6) + decimal(3,2)` results in `decimal(13, 6)`, and then 
`decimal(13, 6) + decimal(12, 5)` results in `decimal(14, 6)`
   
   In the following query:
   ```
   create table foo(a decimal(12, 5), b decimal(12, 6)) using orc
   select sum(coalesce(a+b+ 1.75, a)) from foo
   ```
   At first `coalesce(a+b+ 1.75, a)` is resolved as `coalesce(a+b+ 1.75, cast(a 
as decimal(15, 6))`. In the canonicalized version, the expression becomes 
`coalesce(1.75+b+a, cast(a as decimal(15, 6))`. As explained above, `1.75+b+a` 
is of decimal(14, 6), which is different from  `cast(a as decimal(15, 6)`. Thus 
the following error will happen:
   ```
   java.lang.IllegalArgumentException: requirement failed: All input types must 
be the same except nullable, containsNull, valueContainsNull flags. The input 
types found are
        DecimalType(14,6)
        DecimalType(15,6)
        at scala.Predef$.require(Predef.scala:281)
        at 
org.apache.spark.sql.catalyst.expressions.ComplexTypeMergingExpression.dataTypeCheck(Expression.scala:1149)
        at 
org.apache.spark.sql.catalyst.expressions.ComplexTypeMergingExpression.dataTypeCheck$(Expression.scala:1143)
 
   ```
   This PR is to fix the bug.
   ### Why are the changes needed?
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   Bug fix
   ### Does this PR introduce _any_ user-facing change?
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   No
   ### How was this patch tested?
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   A new test case


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