Fix Round fix issue when input is negative and end with .5

core/src/main/java/com/amazon/opendistroforelasticsearch/sql/expression/operator/arthmetic/MathematicalFunction.java

@@ -422,7 +422,8 @@ private static FunctionResolver round() {
             DOUBLE, FLOAT),
         FunctionDSL.impl(
             FunctionDSL.nullMissingHandling(
-                v -> new ExprDoubleValue((double) Math.round(v.doubleValue()))),
+                v -> new ExprDoubleValue(new BigDecimal(v.doubleValue()).setScale(0,
+                    RoundingMode.HALF_UP).doubleValue())),
             DOUBLE, DOUBLE),
 
         // rand(x, d)

integ-test/src/test/java/com/amazon/opendistroforelasticsearch/sql/sql/MathematicalFunctionIT.java

@@ -101,6 +101,14 @@ public void testRound() throws IOException {
     result = executeQuery("select round(-56, -1)");
     verifySchema(result, schema("round(-56, -1)", null, "long"));
     verifyDataRows(result, rows(-60));
+
+    result = executeQuery("select round(3.5)");
+    verifySchema(result, schema("round(3.5)", null, "double"));
+    verifyDataRows(result, rows(4.0));
+
+    result = executeQuery("select round(-3.5)");
+    verifySchema(result, schema("round(-3.5)", null, "double"));
+    verifyDataRows(result, rows(-4.0));
   }
 
   /**

integ-test/src/test/resources/correctness/expressions/mathematical_functions.txt

@@ -31,6 +31,12 @@ power(2, -2)
 power(2.1, 2)
 power(2, -2.1)
 power(abs(2), 2)
+round(3.4)
+round(3.5)
+round(3.6)
+round(-3.4)
+round(-3.5)
+round(-3.6)
 sign(0)
 sign(-1)
 sign(1)