Update doc

Author: krooswu

core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java

@@ -313,22 +313,19 @@ public Result visit(Join e) {
 
     if (dialect.shouldWrapNestedJoin(e)) {
 
-      if (dialect.shouldWrapNestedJoin(e)) {
-        Set<String> usedNames = new HashSet<>(e.getRowType().getFieldNames());
-
-        // Add both left and right aliases
-        if (leftResult.neededAlias != null) {
-          usedNames.add(leftResult.neededAlias);
-        }
-        if (rightResult.neededAlias != null) {
-          usedNames.add(rightResult.neededAlias);
-        }
+      Set<String> usedNames = new HashSet<>(e.getRowType().getFieldNames());
+      // Add both left and right aliases
+      if (leftResult.neededAlias != null) {
+        usedNames.add(leftResult.neededAlias);
+      }
+      if (rightResult.neededAlias != null) {
+        usedNames.add(rightResult.neededAlias);
+      }
 
-        String safeAlias =
-            SqlValidatorUtil.uniquify("t", usedNames, SqlValidatorUtil.EXPR_SUGGESTER);
+      String safeAlias =
+          SqlValidatorUtil.uniquify("t", usedNames, SqlValidatorUtil.EXPR_SUGGESTER);
 
-        rightResult = wrapNestedJoin(rightResult, e.getRight(), safeAlias);
-      }
+      rightResult = wrapNestedJoin(rightResult, e.getRight(), safeAlias);
     }
 
     final Context leftContext = leftResult.qualifiedContext();