[SPARK-8279][SQL]Add math function round

JIRA: https://issues.apache.org/jira/browse/SPARK-8279

Author: Yijie Shen <henry.yijieshen@gmail.com>

Closes #6938 from yijieshen/udf_round_3 and squashes the following commits:

07a124c [Yijie Shen] remove useless def children
392b65b [Yijie Shen] add negative scale test in DecimalSuite
61760ee [Yijie Shen] address reviews
302a78a [Yijie Shen] Add dataframe function test
31dfe7c [Yijie Shen] refactor round to make it readable
8c7a949 [Yijie Shen] rebase & inputTypes update
9555e35 [Yijie Shen] tiny style fix
d10be4a [Yijie Shen] use TypeCollection to specify wanted input and implicit cast
c3b9839 [Yijie Shen] rely on implict cast to handle string input
b0bff79 [Yijie Shen] make round's inner method's name more meaningful
9bd6930 [Yijie Shen] revert accidental change
e6f44c4 [Yijie Shen] refactor eval and genCode
1b87540 [Yijie Shen] modify checkInputDataTypes using foldable
5486b2d [Yijie Shen] DataFrame API modification
2077888 [Yijie Shen] codegen versioned eval
6cd9a64 [Yijie Shen] refactor Round's constructor
9be894e [Yijie Shen] add round functions in o.a.s.sql.functions
7c83e13 [Yijie Shen] more tests on round
56db4bb [Yijie Shen] Add decimal support to Round
7e163ae [Yijie Shen] style fix
653d047 [Yijie Shen] Add math function round

2 files changed, 47 insertions, 0 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/functions.scala b/sql/core/src/main/scala/org/apache/spark/sql/functions.scala
index 0d4e160ed8..5119ee31d8 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/functions.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/functions.scala
@@ -1390,6 +1390,38 @@ object functions {
   def rint(columnName: String): Column = rint(Column(columnName))
 
   /**
+   * Returns the value of the column `e` rounded to 0 decimal places.
+   *
+   * @group math_funcs
+   * @since 1.5.0
+   */
+  def round(e: Column): Column = round(e.expr, 0)
+
+  /**
+   * Returns the value of the given column rounded to 0 decimal places.
+   *
+   * @group math_funcs
+   * @since 1.5.0
+   */
+  def round(columnName: String): Column = round(Column(columnName), 0)
+
+  /**
+   * Returns the value of `e` rounded to `scale` decimal places.
+   *
+   * @group math_funcs
+   * @since 1.5.0
+   */
+  def round(e: Column, scale: Int): Column = Round(e.expr, Literal(scale))
+
+  /**
+   * Returns the value of the given column rounded to `scale` decimal places.
+   *
+   * @group math_funcs
+   * @since 1.5.0
+   */
+  def round(columnName: String, scale: Int): Column = round(Column(columnName), scale)
+
+  /**
    * Shift the the given value numBits left. If the given value is a long value, this function
    * will return a long value else it will return an integer value.
    *
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/MathExpressionsSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/MathExpressionsSuite.scala
index b30b9f1225..087126bb2e 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/MathExpressionsSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/MathExpressionsSuite.scala
@@ -198,6 +198,21 @@ class MathExpressionsSuite extends QueryTest {
     testOneToOneMathFunction(rint, math.rint)
   }
 
+  test("round") {
+    val df = Seq(5, 55, 555).map(Tuple1(_)).toDF("a")
+    checkAnswer(
+      df.select(round('a), round('a, -1), round('a, -2)),
+      Seq(Row(5, 10, 0), Row(55, 60, 100), Row(555, 560, 600))
+    )
+
+    val pi = 3.1415
+    checkAnswer(
+      ctx.sql(s"SELECT round($pi, -3), round($pi, -2), round($pi, -1), " +
+        s"round($pi, 0), round($pi, 1), round($pi, 2), round($pi, 3)"),
+      Seq(Row(0.0, 0.0, 0.0, 3.0, 3.1, 3.14, 3.142))
+    )
+  }
+
   test("exp") {
     testOneToOneMathFunction(exp, math.exp)
   }