fix bugs with nested column jsonpath parser

processing/src/main/java/org/apache/druid/segment/nested/NestedPathFinder.java

@@ -33,21 +33,20 @@ public class NestedPathFinder
   public static String toNormalizedJsonPath(List<NestedPathPart> paths)
   {
     if (paths.isEmpty()) {
-      return "$.";
+      return "$";
     }
     StringBuilder bob = new StringBuilder();
     boolean first = true;
     for (NestedPathPart partFinder : paths) {
       if (partFinder instanceof NestedPathField) {
         if (first) {
-          bob.append("$.");
-        } else {
-          bob.append(".");
+          bob.append("$");
         }
         final String id = partFinder.getPartIdentifier();
         if (id.contains(".") || id.contains("'") || id.contains("\"") || id.contains("[") || id.contains("]")) {
           bob.append("['").append(id).append("']");
         } else {
+          bob.append(".");
           bob.append(id);
         }
       } else if (partFinder instanceof NestedPathArrayElement) {
@@ -124,16 +123,20 @@ public static List<NestedPathPart> parseJsonPath(@Nullable String path)
         quoteMark = i;
         partMark = i + 1;
       } else if (current == '\'' && quoteMark >= 0 && path.charAt(i - 1) != '\\') {
+        if (path.charAt(i + 1) != ']') {
+          if (arrayMark >= 0) {
+            continue;
+          }
+          badFormatJsonPath(path, "closing ' must immediately precede ']'");
+        }
+
         parts.add(new NestedPathField(getPathSubstring(path, partMark, i)));
         dotMark = -1;
         quoteMark = -1;
         // chomp to next char to eat closing array
         if (++i == path.length()) {
           break;
         }
-        if (path.charAt(i) != ']') {
-          badFormatJsonPath(path, "closing ' must immediately precede ']'");
-        }
         partMark = i + 1;
         arrayMark = -1;
       }

processing/src/test/java/org/apache/druid/frame/segment/FrameStorageAdapterTest.java

@@ -100,6 +100,7 @@ public static Iterable<Object[]> constructorFeeder()
     @Before
     public void setUp()
     {
+
       queryableAdapter = new QueryableIndexStorageAdapter(TestIndex.getMMappedTestIndex());
       frameSegment = FrameTestUtil.adapterToFrameSegment(queryableAdapter, frameType);
       frameAdapter = frameSegment.asStorageAdapter();

processing/src/test/java/org/apache/druid/segment/nested/NestedPathFinderTest.java

@@ -309,9 +309,14 @@ public void testParseJsonPath()
         NestedPathFinder.toNormalizedJqPath(pathParts)
     );
     Assert.assertEquals(
-        "$.['x.y.z][\\']][]'].['13234.12[]][23'].['fo.o'].['.b.a.r.']",
+        "$['x.y.z][\\']][]']['13234.12[]][23']['fo.o']['.b.a.r.']",
         NestedPathFinder.toNormalizedJsonPath(pathParts)
     );
+
+    pathParts = NestedPathFinder.parseJsonPath("$['hell'o']");
+    Assert.assertEquals(1, pathParts.size());
+    Assert.assertEquals("hell'o", pathParts.get(0).getPartIdentifier());
+    Assert.assertEquals("$['hell'o']", NestedPathFinder.toNormalizedJsonPath(pathParts));
   }
 
   @Test

sql/src/test/java/org/apache/druid/sql/calcite/CalciteNestedDataQueryTest.java

@@ -1955,7 +1955,7 @@ public void testGroupByAllPaths() throws Exception
                         .build()
         ),
         ImmutableList.of(
-            new Object[]{"[\"$.\"]", 5L},
+            new Object[]{"[\"$\"]", 5L},
             new Object[]{"[\"$.n.x\",\"$.array[0]\",\"$.array[1]\"]", 2L}
         )
     );