[SPARK-20751][SQL] Add built-in SQL Function - COT

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala

@@ -543,6 +543,28 @@ case class Sqrt(child: Expression) extends UnaryMathExpression(math.sqrt, "SQRT"
   """)
 case class Tan(child: Expression) extends UnaryMathExpression(math.tan, "TAN")
 
+@ExpressionDescription(
+  usage = "_FUNC_(expr) - Returns the cotangent of `expr`.",
+  extended = """
+    Examples:
+      > SELECT _FUNC_(1);
+       0.6420926159343306
+  """)
+case class Cot(child: Expression)
+  extends UnaryMathExpression((x: Double) => 1 / math.tan(x), "COT") {
+  override def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
+    nullSafeCodeGen(ctx, ev, c =>
+      s"""
+        if (${ev.value} == null) {
+          ${ev.isNull} = true;
+        } else {
+          ${ev.value} = 1 / java.lang.Math.tan($c);
+        }
+      """
+    )
+  }
+}
+
 @ExpressionDescription(
   usage = "_FUNC_(expr) - Returns the hyperbolic tangent of `expr`.",
   extended = """

sql/core/src/main/scala/org/apache/spark/sql/functions.scala

@@ -1990,6 +1990,22 @@ object functions {
    */
   def tan(columnName: String): Column = tan(Column(columnName))
 
+  /**
+   * Computes the cotangent of the given column.
+   *
+   * @group math_funcs
+   * @since 2.2.0
+   */
+  def cot(e: Column): Column = withExpr { Cot(e.expr) }
+
+  /**
+   * Computes the cotangent of the given column name.
+   *
+   * @group math_funcs
+   * @since 2.2.0
+   */
+  def cot(colName: String): Column = cot(Column(colName))
+
   /**
    * Computes the hyperbolic tangent of the given value.
    *

sql/core/src/test/scala/org/apache/spark/sql/MathFunctionsSuite.scala

@@ -274,6 +274,10 @@ class MathFunctionsSuite extends QueryTest with SharedSQLContext {
       Row(1, -1))
   }
 
+  test("cot") {
+    testOneToOneMathFunction(cot, (d: Double) => 1 / math.tan(d))
+  }
+
   test("pow / power") {
     testTwoToOneMathFunction(pow, pow, math.pow)