[GitHub] [spark] HyukjinKwon opened a new pull request #24437: [SPARK-27512][SQL] Avoid to replace ', ' in CSV's decimal type inference for backward compatibility

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HyukjinKwon opened a new pull request #24437: [SPARK-27512][SQL] Avoid to replace ',' in CSV's decimal type inference for backward compatibility
URL: https://github.com/apache/spark/pull/24437
 
 
   ## What changes were proposed in this pull request?
   
   The code below currently infers as decimal but previously it was inferred as string.
   
   **In branch-2.4**, type inference path for decimal and parsing data are different.
   
   https://github.com/apache/spark/blob/2a8343121e62aabe5c69d1e20fbb2c01e2e520e7/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/UnivocityParser.scala#L153
   
   https://github.com/apache/spark/blob/c284c4e1f6f684ca8db1cc446fdcc43b46e3413c/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVInferSchema.scala#L125
   
   So the code below:
   
   ```scala
   scala> spark.read.option("delimiter", "|").option("inferSchema", "true").csv(Seq("1,2").toDS).printSchema()
   ```
   
   produced string as its type.
   
   ```
   root
    |-- _c0: string (nullable = true)
   ```
   
   **In the current master**, it now infers decimal as below:
   
   ```
   root
    |-- _c0: decimal(2,0) (nullable = true)
   ```
   
   It happened after https://github.com/apache/spark/pull/22979 because, now after this PR, we only have one way to parse decimal:
   
   https://github.com/apache/spark/blob/7a83d71403edf7d24fa5efc0ef913f3ce76d88b8/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/ExprUtils.scala#L92
   
   **After the fix:**
   
   ```
   root
    |-- _c0: string (nullable = true)
   ```
   
   This PR proposes to restore the previous behaviour back in `CSVInferSchema`.
   
   ## How was this patch tested?
   
   Manually tested and unit tests were added.
   

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