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https://issues.apache.org/jira/browse/SPARK-12128?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15041986#comment-15041986
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Philip Dodds commented on SPARK-12128:
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Hey [~kevinyu98], actually I closed the issue since it was actually down to
the precision doubling up and thus we get a null due to a overflow.
I'm not sure if there is a fix, since it is all down to the default precision
and scale that we set-up, which sort of stops you multiplying them together.
Similar things happen in other DB's but it just took me a while to work it out.
> Multiplication on decimals in dataframe returns null
> ----------------------------------------------------
>
> Key: SPARK-12128
> URL: https://issues.apache.org/jira/browse/SPARK-12128
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 1.5.0, 1.5.1, 1.5.2
> Environment: Scala 2.11/Spark 1.5.0/1.5.1/1.5.2
> Reporter: Philip Dodds
>
> I hit a weird issue when I tried to multiply to decimals in a select (either
> in scala or as SQL), and Im assuming I must be missing the point.
> The issue is fairly easy to recreate with something like the following:
> {code:java}
> val sqlContext = new org.apache.spark.sql.SQLContext(sc)
> import sqlContext.implicits._
> import org.apache.spark.sql.types.Decimal
> case class Trade(quantity: Decimal,price: Decimal)
> val data = Seq.fill(100) {
> val price = Decimal(20+scala.util.Random.nextInt(10))
> val quantity = Decimal(20+scala.util.Random.nextInt(10))
> Trade(quantity, price)
> }
> val trades = sc.parallelize(data).toDF()
> trades.registerTempTable("trades")
> trades.select(trades("price")*trades("quantity")).show
> sqlContext.sql("select
> price/quantity,price*quantity,price+quantity,price-quantity from trades").show
> {code}
> The odd part is if you run it you will see that the addition/division and
> subtraction works but the multiplication returns a null.
> Tested on 1.5.1/1.5.2 (Scala 2.10 and 2.11)
> ie.
> {code}
> +------------------+
> |(price * quantity)|
> +------------------+
> | null|
> | null|
> | null|
> | null|
> | null|
> +------------------+
> +--------------------+----+--------------------+--------------------+
> | _c0| _c1| _c2| _c3|
> +--------------------+----+--------------------+--------------------+
> |0.952380952380952381|null|41.00000000000000...|-1.00000000000000...|
> |1.380952380952380952|null|50.00000000000000...|8.000000000000000000|
> |1.272727272727272727|null|50.00000000000000...|6.000000000000000000|
> |0.833333333333333333|null|44.00000000000000...|-4.00000000000000...|
> |1.000000000000000000|null|58.00000000000000...| 0E-18|
> +--------------------+----+--------------------+--------------------+
> {code}
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