dtenedor commented on code in PR #38419:
URL: https://github.com/apache/spark/pull/38419#discussion_r1093715384


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala:
##########
@@ -331,6 +332,275 @@ case class RoundCeil(child: Expression, scale: Expression)
     copy(child = newLeft, scale = newRight)
 }
 
+
+/**
+ * Truncates a number to the specified number of digits.
+ * @param child
+ *   expression to get the number to be truncated.
+ * @param scale
+ *   expression to get the number of decimal places to truncate to.
+ */
+case class TruncNumber(child: Expression, scale: Expression)
+    extends BaseBinaryExpression
+    with NullIntolerant {
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression,
+      newRight: Expression): TruncNumber = copy(child = newLeft, scale = 
newRight)
+
+  /**
+   * Returns the [[DataType]] of the result of evaluating this expression. It 
is invalid to query
+   * the dataType of an unresolved expression (i.e., when `resolved` == false).
+   */
+  override lazy val dataType: DataType = child.dataType
+
+  /**
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   */
+  override protected def nullSafeEval(input1: Any, input2: Any): Any = {
+    (dataType, input1) match {
+      // Trunc function accepts a second parameter to truncate the input 
number.
+      // If 0, it removes all the decimal values and returns only the integer.
+      // If negative, the number is truncated to the left side of the decimal 
point.
+      // Value  of decimal places to truncate can range from -ve to +ve
+      // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+      // places to truncate is +ve, then we can return that input value 
without any
+      // modification as there is no +ve decimal place to be truncated from an 
integral number
+      // Truncate the input only if the value of decimal places to truncate is 
< 0
+      case (ByteType, input: Byte) if (scaleValue < 0) =>

Review Comment:
   no need for the parentheses around `scaleValue < 0` (here and below)



##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala:
##########
@@ -331,6 +332,275 @@ case class RoundCeil(child: Expression, scale: Expression)
     copy(child = newLeft, scale = newRight)
 }
 
+
+/**
+ * Truncates a number to the specified number of digits.
+ * @param child
+ *   expression to get the number to be truncated.
+ * @param scale
+ *   expression to get the number of decimal places to truncate to.
+ */
+case class TruncNumber(child: Expression, scale: Expression)
+    extends BaseBinaryExpression
+    with NullIntolerant {
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression,
+      newRight: Expression): TruncNumber = copy(child = newLeft, scale = 
newRight)
+
+  /**
+   * Returns the [[DataType]] of the result of evaluating this expression. It 
is invalid to query

Review Comment:
   no need to repeat these comments from the base class if they appear here 
unchanged.



##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala:
##########
@@ -331,6 +332,275 @@ case class RoundCeil(child: Expression, scale: Expression)
     copy(child = newLeft, scale = newRight)
 }
 
+
+/**
+ * Truncates a number to the specified number of digits.
+ * @param child
+ *   expression to get the number to be truncated.
+ * @param scale
+ *   expression to get the number of decimal places to truncate to.
+ */
+case class TruncNumber(child: Expression, scale: Expression)
+    extends BaseBinaryExpression
+    with NullIntolerant {
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression,
+      newRight: Expression): TruncNumber = copy(child = newLeft, scale = 
newRight)
+
+  /**
+   * Returns the [[DataType]] of the result of evaluating this expression. It 
is invalid to query
+   * the dataType of an unresolved expression (i.e., when `resolved` == false).
+   */
+  override lazy val dataType: DataType = child.dataType
+
+  /**
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   */
+  override protected def nullSafeEval(input1: Any, input2: Any): Any = {
+    (dataType, input1) match {
+      // Trunc function accepts a second parameter to truncate the input 
number.
+      // If 0, it removes all the decimal values and returns only the integer.
+      // If negative, the number is truncated to the left side of the decimal 
point.
+      // Value  of decimal places to truncate can range from -ve to +ve
+      // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+      // places to truncate is +ve, then we can return that input value 
without any
+      // modification as there is no +ve decimal place to be truncated from an 
integral number
+      // Truncate the input only if the value of decimal places to truncate is 
< 0
+      case (ByteType, input: Byte) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).toByte
+      case (ShortType, input: Short) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).shortValue
+      case (IntegerType, input: Int) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).intValue
+      case (LongType, input: Long) if (scaleValue < 0) =>
+        TruncNumber.trunc(input, scaleValue).longValue
+      // 2) In the case of Float, Double, and Decimal , TruncNumber.trunc
+      // will accept both -ve and +ve values
+      case (FloatType, input: Float) =>
+        TruncNumber.trunc(input, scaleValue).floatValue
+      case (DoubleType, input: Double) =>
+        TruncNumber.trunc(input, scaleValue).doubleValue
+      case (DecimalType.Fixed(p, s), input: Decimal) =>
+        Decimal(TruncNumber.trunc(input.toJavaBigDecimal, scaleValue), p, s)
+      case _ => input1
+    }
+  }
+
+  /**
+   * Returns Java source code that can be compiled to evaluate this expression.
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   * @param ctx
+   *   a [[CodegenContext]]
+   * @param ev
+   *   an [[ExprCode]] with unique terms.
+   * @return
+   *   an [[ExprCode]] containing the Java source code to generate the given 
expression
+   */
+  override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): 
ExprCode =
+    defineCodeGen(
+      ctx,
+      ev,
+      (input, _) => {
+        val methodName = 
"org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc"
+        // Trunc function accepts a second parameter to truncate the input 
number.
+        // If 0, it removes all the decimal values and returns only the 
integer.
+        // If negative, the number is truncated to the left side of the 
decimal point.
+        // Value  of decimal places to truncate can range from -ve to +ve
+        // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+        // places to truncate is +ve, then we can return that input value 
without any
+        // modification as there is no +ve decimal place to be truncated from 
an integral number
+        // Truncate the input only if the value of decimal places to truncate 
is < 0
+        dataType match {
+          case ByteType if (scaleValue < 0) =>

Review Comment:
   same here



##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala:
##########
@@ -331,6 +332,275 @@ case class RoundCeil(child: Expression, scale: Expression)
     copy(child = newLeft, scale = newRight)
 }
 
+
+/**
+ * Truncates a number to the specified number of digits.
+ * @param child
+ *   expression to get the number to be truncated.
+ * @param scale
+ *   expression to get the number of decimal places to truncate to.
+ */
+case class TruncNumber(child: Expression, scale: Expression)
+    extends BaseBinaryExpression
+    with NullIntolerant {
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression,
+      newRight: Expression): TruncNumber = copy(child = newLeft, scale = 
newRight)
+
+  /**
+   * Returns the [[DataType]] of the result of evaluating this expression. It 
is invalid to query
+   * the dataType of an unresolved expression (i.e., when `resolved` == false).
+   */
+  override lazy val dataType: DataType = child.dataType
+
+  /**
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   */
+  override protected def nullSafeEval(input1: Any, input2: Any): Any = {
+    (dataType, input1) match {
+      // Trunc function accepts a second parameter to truncate the input 
number.
+      // If 0, it removes all the decimal values and returns only the integer.
+      // If negative, the number is truncated to the left side of the decimal 
point.
+      // Value  of decimal places to truncate can range from -ve to +ve
+      // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+      // places to truncate is +ve, then we can return that input value 
without any
+      // modification as there is no +ve decimal place to be truncated from an 
integral number
+      // Truncate the input only if the value of decimal places to truncate is 
< 0
+      case (ByteType, input: Byte) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).toByte
+      case (ShortType, input: Short) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).shortValue
+      case (IntegerType, input: Int) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).intValue
+      case (LongType, input: Long) if (scaleValue < 0) =>
+        TruncNumber.trunc(input, scaleValue).longValue
+      // 2) In the case of Float, Double, and Decimal , TruncNumber.trunc
+      // will accept both -ve and +ve values
+      case (FloatType, input: Float) =>
+        TruncNumber.trunc(input, scaleValue).floatValue
+      case (DoubleType, input: Double) =>
+        TruncNumber.trunc(input, scaleValue).doubleValue
+      case (DecimalType.Fixed(p, s), input: Decimal) =>
+        Decimal(TruncNumber.trunc(input.toJavaBigDecimal, scaleValue), p, s)
+      case _ => input1
+    }
+  }
+
+  /**
+   * Returns Java source code that can be compiled to evaluate this expression.
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   * @param ctx
+   *   a [[CodegenContext]]
+   * @param ev
+   *   an [[ExprCode]] with unique terms.
+   * @return
+   *   an [[ExprCode]] containing the Java source code to generate the given 
expression
+   */
+  override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): 
ExprCode =
+    defineCodeGen(
+      ctx,
+      ev,
+      (input, _) => {
+        val methodName = 
"org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc"
+        // Trunc function accepts a second parameter to truncate the input 
number.
+        // If 0, it removes all the decimal values and returns only the 
integer.
+        // If negative, the number is truncated to the left side of the 
decimal point.
+        // Value  of decimal places to truncate can range from -ve to +ve
+        // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+        // places to truncate is +ve, then we can return that input value 
without any
+        // modification as there is no +ve decimal place to be truncated from 
an integral number
+        // Truncate the input only if the value of decimal places to truncate 
is < 0
+        dataType match {
+          case ByteType if (scaleValue < 0) =>
+            s"""(byte)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case ShortType if (scaleValue < 0) =>
+            s"""(short)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case IntegerType if (scaleValue < 0) =>
+            s"""(int)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case LongType if (scaleValue < 0) =>
+            s"""($methodName(
+               |$input, $scaleValue))""".stripMargin
+          // 2) In the case of Float, Double, and Decimal , TruncNumber.trunc
+          // will accept both -ve and +ve values
+          case FloatType =>
+            s"""$methodName(
+               |$input, $scaleValue).floatValue()""".stripMargin
+          case DoubleType =>
+            s"""$methodName(
+               |$input, $scaleValue).doubleValue()""".stripMargin
+          case DecimalType.Fixed(p, s) =>
+            s"""Decimal.apply(
+               |$methodName(
+               |${input}.toJavaBigDecimal(), $scaleValue), $p, 
$s)""".stripMargin
+          case _ => s"$input"
+        }
+      })
+}
+
+object TruncNumber {
+
+  /**
+   * To truncate whole numbers; byte, short, int, and long types.
+   */
+  def trunc(input: Long, position: Int): Long = {
+    if (position >= 0) {
+      input
+    } else {
+      // Here we truncate the number by the absolute value of the position.
+      // For example, if the input is 123 and the scale is -2, then the result 
is 100.
+      val pow = Math.pow(10, Math.abs(position)).toLong
+      (input / pow) * pow
+    }
+  }
+
+  /**
+   * To truncate double and float type.
+   */
+  def trunc(input: Double, position: Int): BigDecimal = {
+    trunc(jm.BigDecimal.valueOf(input), position)
+  }
+
+  /**
+   * To truncate decimal type.
+   */
+  def trunc(input: jm.BigDecimal, position: Int): jm.BigDecimal = {
+    if (input.scale < position) input
+    else {
+      val wholePart = input.toBigInteger
+      position match {
+        case pos if pos >= 0 =>
+          // Here we truncate only the decimal part by the value of the 
position.
+          val decimalPart = input.remainder(java.math.BigDecimal.ONE)
+          // If the position is zero OR Decimal part is zero,
+          // we extract the whole part and return it.
+          // For example,
+          // if the input is 123.456 and the scale is 0, the result will be 
123.
+          // if the input is 123.000 and the scale is > 0, the result will be 
123.
+          val wholePartBD = new jm.BigDecimal(wholePart)
+          if (pos == 0 || jm.BigDecimal.ZERO.compareTo(decimalPart) == 0) {
+            wholePartBD
+          } else {
+            // To avoid overflow during multiplication, we extract the decimal 
part from the input,
+            // truncate it and then append it to the whole part.
+            // For example, if the input is 123.456 and the scale is 2, the 
result will be 123.45.
+            val pow = jm.BigDecimal.valueOf(Math.pow(10, pos).toLong)
+            val truncated = new 
jm.BigDecimal(decimalPart.multiply(pow).toBigInteger).divide(pow)
+            wholePartBD.add(truncated)
+          }
+        case pos if pos < 0 =>
+          // Here we truncate the whole part by the absolute value of the 
position.
+          // For example, if the input is 123.456 and the scale is -2, the 
result will be 100.
+          val pow = jm.BigInteger.valueOf(Math.pow(10, Math.abs(pos)).toLong)

Review Comment:
   same here



##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala:
##########
@@ -331,6 +332,275 @@ case class RoundCeil(child: Expression, scale: Expression)
     copy(child = newLeft, scale = newRight)
 }
 
+
+/**
+ * Truncates a number to the specified number of digits.
+ * @param child
+ *   expression to get the number to be truncated.
+ * @param scale
+ *   expression to get the number of decimal places to truncate to.
+ */
+case class TruncNumber(child: Expression, scale: Expression)
+    extends BaseBinaryExpression
+    with NullIntolerant {
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression,
+      newRight: Expression): TruncNumber = copy(child = newLeft, scale = 
newRight)
+
+  /**
+   * Returns the [[DataType]] of the result of evaluating this expression. It 
is invalid to query
+   * the dataType of an unresolved expression (i.e., when `resolved` == false).
+   */
+  override lazy val dataType: DataType = child.dataType
+
+  /**
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   */
+  override protected def nullSafeEval(input1: Any, input2: Any): Any = {
+    (dataType, input1) match {
+      // Trunc function accepts a second parameter to truncate the input 
number.
+      // If 0, it removes all the decimal values and returns only the integer.
+      // If negative, the number is truncated to the left side of the decimal 
point.
+      // Value  of decimal places to truncate can range from -ve to +ve
+      // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+      // places to truncate is +ve, then we can return that input value 
without any
+      // modification as there is no +ve decimal place to be truncated from an 
integral number
+      // Truncate the input only if the value of decimal places to truncate is 
< 0
+      case (ByteType, input: Byte) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).toByte
+      case (ShortType, input: Short) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).shortValue
+      case (IntegerType, input: Int) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).intValue
+      case (LongType, input: Long) if (scaleValue < 0) =>
+        TruncNumber.trunc(input, scaleValue).longValue
+      // 2) In the case of Float, Double, and Decimal , TruncNumber.trunc
+      // will accept both -ve and +ve values
+      case (FloatType, input: Float) =>
+        TruncNumber.trunc(input, scaleValue).floatValue
+      case (DoubleType, input: Double) =>
+        TruncNumber.trunc(input, scaleValue).doubleValue
+      case (DecimalType.Fixed(p, s), input: Decimal) =>
+        Decimal(TruncNumber.trunc(input.toJavaBigDecimal, scaleValue), p, s)
+      case _ => input1
+    }
+  }
+
+  /**
+   * Returns Java source code that can be compiled to evaluate this expression.
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   * @param ctx
+   *   a [[CodegenContext]]
+   * @param ev
+   *   an [[ExprCode]] with unique terms.
+   * @return
+   *   an [[ExprCode]] containing the Java source code to generate the given 
expression
+   */
+  override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): 
ExprCode =
+    defineCodeGen(
+      ctx,
+      ev,
+      (input, _) => {
+        val methodName = 
"org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc"
+        // Trunc function accepts a second parameter to truncate the input 
number.
+        // If 0, it removes all the decimal values and returns only the 
integer.
+        // If negative, the number is truncated to the left side of the 
decimal point.
+        // Value  of decimal places to truncate can range from -ve to +ve
+        // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+        // places to truncate is +ve, then we can return that input value 
without any
+        // modification as there is no +ve decimal place to be truncated from 
an integral number
+        // Truncate the input only if the value of decimal places to truncate 
is < 0
+        dataType match {
+          case ByteType if (scaleValue < 0) =>
+            s"""(byte)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case ShortType if (scaleValue < 0) =>
+            s"""(short)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case IntegerType if (scaleValue < 0) =>
+            s"""(int)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case LongType if (scaleValue < 0) =>
+            s"""($methodName(
+               |$input, $scaleValue))""".stripMargin
+          // 2) In the case of Float, Double, and Decimal , TruncNumber.trunc
+          // will accept both -ve and +ve values
+          case FloatType =>
+            s"""$methodName(
+               |$input, $scaleValue).floatValue()""".stripMargin
+          case DoubleType =>
+            s"""$methodName(
+               |$input, $scaleValue).doubleValue()""".stripMargin
+          case DecimalType.Fixed(p, s) =>
+            s"""Decimal.apply(
+               |$methodName(
+               |${input}.toJavaBigDecimal(), $scaleValue), $p, 
$s)""".stripMargin
+          case _ => s"$input"
+        }
+      })
+}
+
+object TruncNumber {
+
+  /**
+   * To truncate whole numbers; byte, short, int, and long types.
+   */
+  def trunc(input: Long, position: Int): Long = {
+    if (position >= 0) {
+      input
+    } else {
+      // Here we truncate the number by the absolute value of the position.
+      // For example, if the input is 123 and the scale is -2, then the result 
is 100.
+      val pow = Math.pow(10, Math.abs(position)).toLong
+      (input / pow) * pow
+    }
+  }
+
+  /**
+   * To truncate double and float type.
+   */
+  def trunc(input: Double, position: Int): BigDecimal = {
+    trunc(jm.BigDecimal.valueOf(input), position)
+  }
+
+  /**
+   * To truncate decimal type.
+   */
+  def trunc(input: jm.BigDecimal, position: Int): jm.BigDecimal = {
+    if (input.scale < position) input
+    else {
+      val wholePart = input.toBigInteger
+      position match {
+        case pos if pos >= 0 =>
+          // Here we truncate only the decimal part by the value of the 
position.
+          val decimalPart = input.remainder(java.math.BigDecimal.ONE)
+          // If the position is zero OR Decimal part is zero,
+          // we extract the whole part and return it.
+          // For example,
+          // if the input is 123.456 and the scale is 0, the result will be 
123.
+          // if the input is 123.000 and the scale is > 0, the result will be 
123.
+          val wholePartBD = new jm.BigDecimal(wholePart)
+          if (pos == 0 || jm.BigDecimal.ZERO.compareTo(decimalPart) == 0) {
+            wholePartBD
+          } else {
+            // To avoid overflow during multiplication, we extract the decimal 
part from the input,
+            // truncate it and then append it to the whole part.
+            // For example, if the input is 123.456 and the scale is 2, the 
result will be 123.45.
+            val pow = jm.BigDecimal.valueOf(Math.pow(10, pos).toLong)

Review Comment:
   looks like this logic is duplicated with L457-458, can we dedup it to one 
place?



##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala:
##########
@@ -331,6 +332,275 @@ case class RoundCeil(child: Expression, scale: Expression)
     copy(child = newLeft, scale = newRight)
 }
 
+
+/**
+ * Truncates a number to the specified number of digits.
+ * @param child
+ *   expression to get the number to be truncated.
+ * @param scale
+ *   expression to get the number of decimal places to truncate to.
+ */
+case class TruncNumber(child: Expression, scale: Expression)
+    extends BaseBinaryExpression
+    with NullIntolerant {
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression,
+      newRight: Expression): TruncNumber = copy(child = newLeft, scale = 
newRight)
+
+  /**
+   * Returns the [[DataType]] of the result of evaluating this expression. It 
is invalid to query
+   * the dataType of an unresolved expression (i.e., when `resolved` == false).
+   */
+  override lazy val dataType: DataType = child.dataType
+
+  /**
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   */
+  override protected def nullSafeEval(input1: Any, input2: Any): Any = {
+    (dataType, input1) match {
+      // Trunc function accepts a second parameter to truncate the input 
number.
+      // If 0, it removes all the decimal values and returns only the integer.
+      // If negative, the number is truncated to the left side of the decimal 
point.
+      // Value  of decimal places to truncate can range from -ve to +ve
+      // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+      // places to truncate is +ve, then we can return that input value 
without any
+      // modification as there is no +ve decimal place to be truncated from an 
integral number
+      // Truncate the input only if the value of decimal places to truncate is 
< 0
+      case (ByteType, input: Byte) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).toByte
+      case (ShortType, input: Short) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).shortValue
+      case (IntegerType, input: Int) if (scaleValue < 0) =>
+        TruncNumber.trunc(input.toLong, scaleValue).intValue
+      case (LongType, input: Long) if (scaleValue < 0) =>
+        TruncNumber.trunc(input, scaleValue).longValue
+      // 2) In the case of Float, Double, and Decimal , TruncNumber.trunc
+      // will accept both -ve and +ve values
+      case (FloatType, input: Float) =>
+        TruncNumber.trunc(input, scaleValue).floatValue
+      case (DoubleType, input: Double) =>
+        TruncNumber.trunc(input, scaleValue).doubleValue
+      case (DecimalType.Fixed(p, s), input: Decimal) =>
+        Decimal(TruncNumber.trunc(input.toJavaBigDecimal, scaleValue), p, s)
+      case _ => input1
+    }
+  }
+
+  /**
+   * Returns Java source code that can be compiled to evaluate this expression.
+   * This overridden implementation delegates the overloaded TruncNumber.trunc 
methods based on
+   * data type of input values
+   * @param ctx
+   *   a [[CodegenContext]]
+   * @param ev
+   *   an [[ExprCode]] with unique terms.
+   * @return
+   *   an [[ExprCode]] containing the Java source code to generate the given 
expression
+   */
+  override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): 
ExprCode =
+    defineCodeGen(
+      ctx,
+      ev,
+      (input, _) => {
+        val methodName = 
"org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc"
+        // Trunc function accepts a second parameter to truncate the input 
number.
+        // If 0, it removes all the decimal values and returns only the 
integer.
+        // If negative, the number is truncated to the left side of the 
decimal point.
+        // Value  of decimal places to truncate can range from -ve to +ve
+        // 1) In the case of integral numbers, as there is no decimal part if 
the value of decimal
+        // places to truncate is +ve, then we can return that input value 
without any
+        // modification as there is no +ve decimal place to be truncated from 
an integral number
+        // Truncate the input only if the value of decimal places to truncate 
is < 0
+        dataType match {
+          case ByteType if (scaleValue < 0) =>
+            s"""(byte)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case ShortType if (scaleValue < 0) =>
+            s"""(short)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case IntegerType if (scaleValue < 0) =>
+            s"""(int)($methodName(
+               |(long)$input, $scaleValue))""".stripMargin
+          case LongType if (scaleValue < 0) =>
+            s"""($methodName(
+               |$input, $scaleValue))""".stripMargin
+          // 2) In the case of Float, Double, and Decimal , TruncNumber.trunc
+          // will accept both -ve and +ve values
+          case FloatType =>
+            s"""$methodName(
+               |$input, $scaleValue).floatValue()""".stripMargin
+          case DoubleType =>
+            s"""$methodName(
+               |$input, $scaleValue).doubleValue()""".stripMargin
+          case DecimalType.Fixed(p, s) =>
+            s"""Decimal.apply(
+               |$methodName(
+               |${input}.toJavaBigDecimal(), $scaleValue), $p, 
$s)""".stripMargin
+          case _ => s"$input"
+        }
+      })
+}
+
+object TruncNumber {
+
+  /**
+   * To truncate whole numbers; byte, short, int, and long types.
+   */
+  def trunc(input: Long, position: Int): Long = {
+    if (position >= 0) {
+      input
+    } else {
+      // Here we truncate the number by the absolute value of the position.
+      // For example, if the input is 123 and the scale is -2, then the result 
is 100.
+      val pow = Math.pow(10, Math.abs(position)).toLong
+      (input / pow) * pow
+    }
+  }
+
+  /**
+   * To truncate double and float type.
+   */
+  def trunc(input: Double, position: Int): BigDecimal = {
+    trunc(jm.BigDecimal.valueOf(input), position)
+  }
+
+  /**
+   * To truncate decimal type.
+   */
+  def trunc(input: jm.BigDecimal, position: Int): jm.BigDecimal = {
+    if (input.scale < position) input
+    else {
+      val wholePart = input.toBigInteger
+      position match {
+        case pos if pos >= 0 =>
+          // Here we truncate only the decimal part by the value of the 
position.
+          val decimalPart = input.remainder(java.math.BigDecimal.ONE)
+          // If the position is zero OR Decimal part is zero,
+          // we extract the whole part and return it.
+          // For example,
+          // if the input is 123.456 and the scale is 0, the result will be 
123.
+          // if the input is 123.000 and the scale is > 0, the result will be 
123.
+          val wholePartBD = new jm.BigDecimal(wholePart)
+          if (pos == 0 || jm.BigDecimal.ZERO.compareTo(decimalPart) == 0) {
+            wholePartBD
+          } else {
+            // To avoid overflow during multiplication, we extract the decimal 
part from the input,
+            // truncate it and then append it to the whole part.
+            // For example, if the input is 123.456 and the scale is 2, the 
result will be 123.45.
+            val pow = jm.BigDecimal.valueOf(Math.pow(10, pos).toLong)
+            val truncated = new 
jm.BigDecimal(decimalPart.multiply(pow).toBigInteger).divide(pow)
+            wholePartBD.add(truncated)
+          }
+        case pos if pos < 0 =>
+          // Here we truncate the whole part by the absolute value of the 
position.
+          // For example, if the input is 123.456 and the scale is -2, the 
result will be 100.
+          val pow = jm.BigInteger.valueOf(Math.pow(10, Math.abs(pos)).toLong)
+          new jm.BigDecimal(wholePart.divide(pow).multiply(pow), 0)
+      }
+    }
+  }
+}
+
+// scalastyle:off line.size.limit
+@ExpressionDescription(
+  usage = """_FUNC_(number[, position]) - Returns the number after truncating 
to the specified number of digits.
+    An optional `position` parameter can be specified to truncate digits to 
the right of the decimal point.
+    If 0, it removes all the decimal values and returns only the integer.
+    If negative, the number is truncated to the left side of the decimal point.
+    Note that there is an overloaded version of this function to truncate date 
values.
+    _FUNC_(date, fmt) - Returns `date` with the time portion of the day 
truncated to the unit specified by the format model `fmt`.
+  """,
+  arguments = """
+    Arguments:
+      * number - number to be truncated
+      * position - number of decimal places up to which the given number is to 
be truncated
+    Arguments: To truncate date values:
+      * date - date value or valid date string
+      * fmt - the format representing the unit to be truncated to
+          - "YEAR", "YYYY", "YY" - truncate to the first date of the year that 
the `date` falls in
+          - "QUARTER" - truncate to the first date of the quarter that the 
`date` falls in
+          - "MONTH", "MM", "MON" - truncate to the first date of the month 
that the `date` falls in
+          - "WEEK" - truncate to the Monday of the week that the `date` falls 
in
+  """,
+  examples = """
+    Examples:
+      > SELECT _FUNC_('2019-08-04', 'week');
+       2019-07-29
+      > SELECT _FUNC_('2019-08-04', 'quarter');
+       2019-07-01
+      > SELECT _FUNC_('2009-02-12', 'MM');
+       2009-02-01
+      > SELECT _FUNC_('2015-10-27', 'YEAR');
+       2015-01-01
+      > SELECT _FUNC_(-10.11, 0);
+       -10.00
+      > SELECT _FUNC_(10.11, -1);
+       10.00
+      > SELECT _FUNC_(100.61, 0);
+       100.00
+      > SELECT _FUNC_(-19087.1560, -3);
+       -19000.0000
+      > SELECT _FUNC_(10876.5489, -1);
+       10870.0000
+      > SELECT _FUNC_(-7767.1160, 2);
+       -7767.1100
+      > SELECT _FUNC_(17646.6019, 3);
+       17646.6010
+  """,
+  since = "3.5.0",
+  group = "math_funcs")
+// scalastyle:on line.size.limit
+object TruncExpressionBuilder extends ExpressionBuilder {
+  override def build(funcName: String, expressions: Seq[Expression]): 
Expression = {
+    val numArgs = expressions.length
+    if (numArgs < 1) {
+      throw QueryCompilationErrors.invalidFunctionArgumentNumberError(Seq(2), 
funcName, numArgs)
+    }
+    expressions(0).dataType match {
+      case ByteType | ShortType | IntegerType | LongType | FloatType | 
DoubleType |
+          DecimalType.Fixed(_, _) =>
+        buildTruncNumber(funcName, expressions)
+      case _ => buildTruncDate(funcName, expressions)
+    }
+  }
+
+  private def buildTruncDate(funcName: String, expressions: Seq[Expression]) = 
{
+    val numArgs = expressions.length
+    if (numArgs == 2) {
+      TruncDate(expressions(0), expressions(1))
+    } else {
+      throw QueryCompilationErrors.invalidFunctionArgumentNumberError(Seq(2), 
funcName, numArgs)
+    }
+  }
+
+  private def buildTruncNumber(funcName: String, expressions: Seq[Expression]) 
= {
+    val numArgs = expressions.length
+    if (numArgs < 1) {
+      throw QueryCompilationErrors.invalidFunctionArgumentNumberError(Seq(2), 
funcName, numArgs)
+    }
+    val position = if (numArgs == 2) {
+      val positionExpr = expressions(1)
+      val scale_value = positionExpr.eval()
+      if (!(positionExpr.foldable && positionExpr.dataType == IntegerType) ||

Review Comment:
   ```suggestion
         if (!positionExpr.foldable || positionExpr.dataType != IntegerType ||
   ```



##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala:
##########
@@ -331,6 +332,268 @@ case class RoundCeil(child: Expression, scale: Expression)
     copy(child = newLeft, scale = newRight)
 }
 
+case class TruncNumber(child: Expression, scale: Expression)
+  extends BaseBinaryExpression with NullIntolerant {
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression,
+      newRight: Expression): TruncNumber = copy(child = newLeft, scale = 
newRight)
+
+  /**
+   * Returns Java source code that can be compiled to evaluate this 
expression. The default
+   * behavior is to call the eval method of the expression. Concrete 
expression implementations
+   * should override this to do actual code generation.
+   *
+   * @param ctx
+   *   a [[CodegenContext]]
+   * @param ev
+   *   an [[ExprCode]] with unique terms.
+   * @return
+   *   an [[ExprCode]] containing the Java source code to generate the given 
expression
+   */
+  override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): 
ExprCode =
+    defineCodeGen(
+      ctx,
+      ev,
+      (input, _) => {
+        dataType match {
+          case ByteType if (_scale <= 0) =>
+            
s"""(byte)(org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc(
+             |(long)$input, ${_scale}))""".stripMargin
+          case ShortType if (_scale <= 0) =>
+            
s"""(short)(org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc(
+             |(long)$input, ${_scale}))""".stripMargin
+          case IntegerType if (_scale <= 0) =>
+            
s"""(int)(org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc(
+             |(long)$input, ${_scale}))""".stripMargin
+          case LongType if (_scale <= 0) =>
+            s"""(org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc(
+             |$input, ${_scale}))""".stripMargin
+          case FloatType if (_scale <= 0) =>
+            s"""org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc(
+             |$input, ${_scale}).floatValue()""".stripMargin
+          case DoubleType if (_scale <= 0) =>
+            s"""org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc(
+             |$input, ${_scale}).doubleValue()""".stripMargin
+          case DecimalType.Fixed(_, _) =>
+            s"""Decimal.apply(
+             |org.apache.spark.sql.catalyst.expressions.TruncNumber.trunc(
+             |${input}.toJavaBigDecimal(), ${_scale}))""".stripMargin
+          case _ => s"$input"
+        }
+      })
+
+  /**
+   * Returns the [[DataType]] of the result of evaluating this expression. It 
is invalid to query
+   * the dataType of an unresolved expression (i.e., when `resolved` == false).
+   */
+  override lazy val dataType: DataType = {
+    child.dataType match {
+      case DecimalType.Fixed(p, s) =>
+        val newPosition =
+          if (_scale > 0) {
+            if (_scale >= s) {
+              s
+            } else {
+              _scale
+            }
+          } else {
+            0
+          }
+        DecimalType(p - s + newPosition, newPosition)
+      case t => t
+    }
+  }
+
+  /**
+   * Called by default [[eval]] implementation. If subclass of 
BinaryExpression keep the default
+   * nullability, they can override this method to save null-check code. If we 
need full control
+   * of evaluation process, we should override [[eval]].
+   */
+  override protected def nullSafeEval(input1: Any, input2: Any): Any = {
+    dataType match {
+      case ByteType if (_scale <= 0) =>
+        TruncNumber.trunc(input1.asInstanceOf[Byte].toLong, _scale).toByte
+      case ShortType if (_scale <= 0) =>
+        TruncNumber.trunc(input1.asInstanceOf[Short].toLong, _scale).shortValue
+      case IntegerType if (_scale <= 0) =>
+        TruncNumber.trunc(input1.asInstanceOf[Int].toLong, _scale).intValue
+      case LongType if (_scale <= 0) =>
+        TruncNumber.trunc(input1.asInstanceOf[Long], _scale).longValue
+      case FloatType =>
+        TruncNumber.trunc(input1.asInstanceOf[Float], _scale).floatValue
+      case DoubleType =>
+        TruncNumber.trunc(input1.asInstanceOf[Double], _scale).doubleValue
+      case DecimalType.Fixed(p, s) =>
+        
Decimal(TruncNumber.trunc(input1.asInstanceOf[Decimal].toJavaBigDecimal, 
_scale))
+      case _ => input1
+    }
+  }
+}
+
+object TruncNumber {
+  /**
+   * To truncate whole numbers ; byte, short, int, long types
+   */
+  def trunc(input: Long, position: Int): Long = {
+    if (position >= 0) {
+      input
+    } else {
+      // position is -ve, truncate the number by absolute value of position
+      // eg: input 123 , scale -2 , result 100
+      val pow = Math.pow(10, Math.abs(position)).toLong
+      (input / pow) * pow
+    }
+  }
+
+  /**
+   * To truncate double and float type
+   */
+  def trunc(input: Double, position: Int): BigDecimal = {
+    trunc(jm.BigDecimal.valueOf(input), position)
+  }
+
+  /**
+   * To truncate decimal type
+   */
+  def trunc(input: jm.BigDecimal, position: Int): jm.BigDecimal = {
+    if (input.scale < position) {
+      input
+    } else {
+      val wholePart = input.toBigInteger
+      if (position > 0) {
+        // position is +ve , truncate only the decimal part by value of 
position
+        val pow = jm.BigDecimal.valueOf(Math.pow(10, position).toLong)
+        val decimalPart = input.remainder(java.math.BigDecimal.ONE)
+        // To avoid overflow while multiplication, extract decimal part first,
+        // truncate it and then add it to whole part
+        // eg: input 123.456, scale 2, result 123.45
+        if (jm.BigDecimal.ZERO.compareTo(decimalPart) == 0) {
+          new jm.BigDecimal(wholePart)
+        } else {
+          val newRemainder = new 
jm.BigDecimal(decimalPart.multiply(pow).toBigInteger).divide(pow)
+          new jm.BigDecimal(wholePart).add(newRemainder)
+        }
+      } else if (position == 0) {
+        // position is 0, extract whole part
+        // eg: input 123.456, scale 0, result 123
+        new jm.BigDecimal(wholePart)
+      } else {
+        // position is -ve, truncate the whole part by absolute value of 
position
+        // eg: input 123.456, scale -2, result 100
+        if (jm.BigInteger.ZERO.compareTo(wholePart) == 0) {
+          new jm.BigDecimal(wholePart)
+        } else {
+          val pow = jm.BigInteger.valueOf(Math.pow(10, 
Math.abs(position)).toLong)
+          new jm.BigDecimal(wholePart.divide(pow).multiply(pow), 0)
+        }
+      }
+    }
+  }
+}
+
+// scalastyle:off line.size.limit
+@ExpressionDescription(
+  usage = """_FUNC_(number[, position]) - Returns the number after truncated 
to the specified places.
+    An optional `position` parameter can be specified to truncate digits to 
the right of the decimal point.
+    If 0, it removes all the decimal values and returns only the integer.
+    If negative, the number is truncated to the left side of the decimal point.
+    There is an overloaded version of this function to truncate date values
+    _FUNC_(date, fmt) - Returns `date` with the time portion of the day 
truncated to the unit specified by the format model `fmt`.
+  """,
+  arguments = """
+    Arguments:
+      * number - number to be truncated
+      * position - number of decimal places up to which the given number is to 
be truncated
+    Arguments: To truncate date value:
+      * date - date value or valid date string
+      * fmt - the format representing the unit to be truncated to
+          - "YEAR", "YYYY", "YY" - truncate to the first date of the year that 
the `date` falls in
+          - "QUARTER" - truncate to the first date of the quarter that the 
`date` falls in
+          - "MONTH", "MM", "MON" - truncate to the first date of the month 
that the `date` falls in
+          - "WEEK" - truncate to the Monday of the week that the `date` falls 
in
+  """,
+  examples = """
+    Examples:
+      > SELECT _FUNC_('2019-08-04', 'week');
+       2019-07-29
+      > SELECT _FUNC_('2019-08-04', 'quarter');
+       2019-07-01
+      > SELECT _FUNC_('2009-02-12', 'MM');
+       2009-02-01
+      > SELECT _FUNC_('2015-10-27', 'YEAR');
+       2015-01-01
+      > SELECT _FUNC_(-10.11, 0);
+       -10
+      > SELECT _FUNC_(10.11, -1);
+       10
+      > SELECT _FUNC_(100.61, 0);
+       100
+      > SELECT _FUNC_(-19087.1560, -3);
+       -19000
+      > SELECT _FUNC_(10876.5489, -1);
+       10870
+      > SELECT _FUNC_(-7767.1160, 2);
+       -7767.11
+      > SELECT _FUNC_(17646.6019, 3);
+       17646.601
+  """,
+  since = "3.4.0",
+  group = "math_funcs")
+// scalastyle:on line.size.limit
+object TruncExpressionBuilder extends ExpressionBuilder {
+  override def build(funcName: String, expressions: Seq[Expression]): 
Expression = {
+    val numArgs = expressions.length
+    if (numArgs >= 1) {
+      expressions(0).dataType match {
+        case ByteType |  ShortType | IntegerType | LongType | FloatType | 
DoubleType
+             | DecimalType.Fixed(_, _) => buildTruncNumber(funcName, 
expressions)
+        case _ => buildTruncDate(funcName, expressions)
+      }
+    } else {
+      throw QueryCompilationErrors.invalidFunctionArgumentNumberError(Seq(2), 
funcName, numArgs)
+    }
+  }
+
+  private def buildTruncDate(funcName: String, expressions: Seq[Expression]) = 
{
+    val numArgs = expressions.length
+    if (numArgs == 2) {
+      TruncDate(expressions(0), expressions(1))
+    } else {
+      throw QueryCompilationErrors.invalidFunctionArgumentNumberError(Seq(2), 
funcName, numArgs)

Review Comment:
   This change does not seem to be reflected on GitHub; did you forget to push 
a commit?



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