[BugFix] fix concat_ws(',', 1, NULL) incorrect result when last element is NULL (backport #56384) (#56456)

Co-authored-by: kaijianding <[email protected]>

Author: mergify[bot]

fe/fe-core/src/main/java/com/starrocks/sql/optimizer/rewrite/ScalarOperatorFunctions.java

@@ -77,10 +77,12 @@
 import java.time.temporal.IsoFields;
 import java.time.temporal.TemporalAdjusters;
 import java.time.temporal.TemporalUnit;
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import static com.starrocks.catalog.PrimitiveType.BIGINT;
 import static com.starrocks.catalog.PrimitiveType.BITMAP;
@@ -1297,15 +1299,13 @@ public static ConstantOperator concat_ws(ConstantOperator split, ConstantOperato
         if (split.isNull()) {
             return ConstantOperator.createNull(Type.VARCHAR);
         }
-        final StringBuilder resultBuilder = new StringBuilder();
-        for (int i = 0; i < values.length - 1; i++) {
-            if (values[i].isNull()) {
-                continue;
-            }
-            resultBuilder.append(values[i].getVarchar()).append(split.getVarchar());
-        }
-        resultBuilder.append(values[values.length - 1].getVarchar());
-        return ConstantOperator.createVarchar(resultBuilder.toString());
+        String separator = split.getVarchar();
+        return ConstantOperator.createVarchar(
+                Arrays.stream(values)
+                        .filter(v -> !v.isNull())
+                        .map(ConstantOperator::getVarchar)
+                        .collect(Collectors.joining(separator))
+        );
     }
 
     @ConstantFunction(name = "version", argTypes = {}, returnType = VARCHAR)

fe/fe-core/src/test/java/com/starrocks/sql/optimizer/rewrite/ScalarOperatorFunctionsTest.java

@@ -1322,22 +1322,42 @@ public void concat_ws() {
 
     @Test
     public void concat_ws_with_null() {
-        ConstantOperator[] argWithNull = {ConstantOperator.createVarchar("star"),
-                ConstantOperator.createNull(Type.VARCHAR),
-                ConstantOperator.createVarchar("cks")};
-        ConstantOperator result =
-                ScalarOperatorFunctions.concat_ws(ConstantOperator.createVarchar("ro"), argWithNull);
-        assertEquals(Type.VARCHAR, result.getType());
-        assertEquals("starrocks", result.getVarchar());
-
-        result = ScalarOperatorFunctions.concat_ws(ConstantOperator.createVarchar(","),
-                ConstantOperator.createNull(Type.VARCHAR));
-        assertEquals("", result.getVarchar());
-
-        ConstantOperator[] argWithoutNull = {ConstantOperator.createVarchar("star"),
-                ConstantOperator.createVarchar("cks")};
-        result = ScalarOperatorFunctions.concat_ws(ConstantOperator.createNull(Type.VARCHAR), argWithoutNull);
-        assertTrue(result.isNull());
+        {
+            ConstantOperator[] argWithNull = {ConstantOperator.createVarchar("star"),
+                    ConstantOperator.createNull(Type.VARCHAR),
+                    ConstantOperator.createVarchar("cks")};
+            ConstantOperator result =
+                    ScalarOperatorFunctions.concat_ws(ConstantOperator.createVarchar("ro"), argWithNull);
+            assertEquals(Type.VARCHAR, result.getType());
+            assertEquals("starrocks", result.getVarchar());
+        }
+        {
+            ConstantOperator[] argWithNull = {ConstantOperator.createVarchar("1"),
+                    ConstantOperator.createNull(Type.VARCHAR)};
+            ConstantOperator result =
+                    ScalarOperatorFunctions.concat_ws(ConstantOperator.createVarchar(","), argWithNull);
+            assertEquals(Type.VARCHAR, result.getType());
+            assertEquals("1", result.getVarchar());
+        }
+        {
+            ConstantOperator[] argWithNull = {ConstantOperator.createVarchar("1"),
+                    ConstantOperator.createNull(Type.VARCHAR),
+                    ConstantOperator.createNull(Type.VARCHAR)};
+            ConstantOperator result =
+                    ScalarOperatorFunctions.concat_ws(ConstantOperator.createVarchar(","), argWithNull);
+            assertEquals(Type.VARCHAR, result.getType());
+            assertEquals("1", result.getVarchar());
+        }
+        {
+            ConstantOperator result = ScalarOperatorFunctions.concat_ws(ConstantOperator.createVarchar(","),
+                    ConstantOperator.createNull(Type.VARCHAR));
+            assertEquals("", result.getVarchar());
+
+            ConstantOperator[] argWithoutNull = {ConstantOperator.createVarchar("star"),
+                    ConstantOperator.createVarchar("cks")};
+            result = ScalarOperatorFunctions.concat_ws(ConstantOperator.createNull(Type.VARCHAR), argWithoutNull);
+            assertTrue(result.isNull());
+        }
     }
 
     @Test