Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/20023#discussion_r162246614
--- Diff: docs/sql-programming-guide.md ---
@@ -1795,6 +1795,11 @@ options.
- Since Spark 2.3, when all inputs are binary, SQL `elt()` returns an
output as binary. Otherwise, it returns as a string. Until Spark 2.3, it always
returns as a string despite of input types. To keep the old behavior, set
`spark.sql.function.eltOutputAsString` to `true`.
+ - Since Spark 2.3, by default arithmetic operations between decimals
return a rounded value if an exact representation is not possible. This is
compliant to SQL standards and Hive's behavior introduced in HIVE-15331. This
involves the following changes
+ - The rules to determine the result type of an arithmetic operation
have been updated. In particular, if the precision / scale needed are out of
the range of available values, the scale is reduced up to 6, in order to
prevent the truncation of the integer part of the decimals.
+ - Literal values used in SQL operations are converted to DECIMAL with
the exact precision and scale needed by them.
+ - The configuration `spark.sql.decimalOperations.allowPrecisionLoss`
has been introduced. It defaults to `true`, which means the new behavior
described here; if set to `false`, Spark will use the previous rules and
behavior.
--- End diff --
At least, we need to say, NULL will be returned in this case.
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