diff --git a/docs/design/2018-08-29-new-planner.md b/docs/design/2018-08-29-new-planner.md
index c0b26bd041618..1bdd6e693164c 100644
--- a/docs/design/2018-08-29-new-planner.md
+++ b/docs/design/2018-08-29-new-planner.md
@@ -61,6 +61,8 @@ operator.
   With the concept of **Group** and **Group Expression**, all the logically
   equivalent expressions can be stored in a root Group.
 
+  ![group and expression](./group-and-expression.png)
+
 - **Transformation Rule**
 
   The transform rule is used to transform a logical plan to another equivalent
diff --git a/docs/design/group-and-expression.png b/docs/design/group-and-expression.png
new file mode 100644
index 0000000000000..eaac174a4afd6
Binary files /dev/null and b/docs/design/group-and-expression.png differ