[SPARK-8363][SQL] Move sqrt to math and extend UnaryMathExpression

JIRA: https://issues.apache.org/jira/browse/SPARK-8363

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #6823 from viirya/move_sqrt and squashes the following commits:

8977e11 [Liang-Chi Hsieh] Remove unnecessary old tests.
d23e79e [Liang-Chi Hsieh] Explicitly indicate sqrt value sequence.
699f48b [Liang-Chi Hsieh] Use correct @since tag.
8dff6d1 [Liang-Chi Hsieh] Merge remote-tracking branch 'upstream/master' into move_sqrt
bc2ed77 [Liang-Chi Hsieh] Remove/move arithmetic expression test and expression type checking test. Remove unnecessary Sqrt type rule.
d38492f [Liang-Chi Hsieh] Now sqrt accepts boolean because type casting is handled by HiveTypeCoercion.
297cc90 [Liang-Chi Hsieh] Sqrt only accepts double input.
ef4a21a [Liang-Chi Hsieh] Move sqrt to math.

2 files changed, 19 insertions, 1 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 dff0932c45..d8a91bead7 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
@@ -707,12 +707,20 @@ object functions {
   /**
    * Computes the square root of the specified float value.
    *
-   * @group normal_funcs
+   * @group math_funcs
    * @since 1.3.0
    */
   def sqrt(e: Column): Column = Sqrt(e.expr)
 
   /**
+   * Computes the square root of the specified float value.
+   *
+   * @group math_funcs
+   * @since 1.5.0
+   */
+  def sqrt(colName: String): Column = sqrt(Column(colName))
+
+  /**
    * Creates a new struct column. The input column must be a column in a [[DataFrame]], or
    * a derived column expression that is named (i.e. aliased).
    *
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 7c9c121b95..2768d7dfc8 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
@@ -270,6 +270,16 @@ class MathExpressionsSuite extends QueryTest {
     checkAnswer(ctx.sql("SELECT LOG2(8), LOG2(null)"), Row(3, null))
   }
 
+  test("sqrt") {
+    val df = Seq((1, 4)).toDF("a", "b")
+    checkAnswer(
+      df.select(sqrt("a"), sqrt("b")),
+      Row(1.0, 2.0))
+
+    checkAnswer(ctx.sql("SELECT SQRT(4.0), SQRT(null)"), Row(2.0, null))
+    checkAnswer(df.selectExpr("sqrt(a)", "sqrt(b)", "sqrt(null)"), Row(1.0, 2.0, null))
+  }
+
   test("negative") {
     checkAnswer(
       ctx.sql("SELECT negative(1), negative(0), negative(-1)"),