[GitHub] [spark] cloud-fan commented on a change in pull request #26716: [SPARK-30083][SQL] visitArithmeticUnary should wrap PLUS case with UnaryPositive for type checking

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cloud-fan commented on a change in pull request #26716: [SPARK-30083][SQL] visitArithmeticUnary should wrap PLUS case with UnaryPositive for type checking
URL: https://github.com/apache/spark/pull/26716#discussion_r352999849
 
 

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 File path: docs/sql-migration-guide.md
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 @@ -254,6 +254,8 @@ license: |
         </tr>
     </table>
 
+    - Since Spark 3.0, the unary arithmetic operator plus(`+`) only accepts string, numeric and interval type values as inputs. Besides, `+` with a integral string representation will be coerced to double value, e.g. `+'1'` results `1.0`. In Spark version 2.4 and earlier,  there is no type checking for it, thus, all type values with a `+` prefix are valid, e.g. `+ array(1, 2)` is valid and results `[1, 2]`. Besides, there is no implicit type coercion for `+` with string, e.g. `+'1'` results `1`.
+
 
 Review comment:
   in 2.4, `+'1'` results to string `'1'`.

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