update lookup

docs-2.0/3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md

@@ -43,6 +43,7 @@ RETURN
 DESCRIBE
 DESC
 VERTEX
+VERTICES
 EDGE
 EDGES
 UPDATE

docs-2.0/3.ngql-guide/7.general-query-statements/5.lookup.md

@@ -1,5 +1,7 @@
 # LOOKUP
 
+<!-- This topic needs to be modified after compulsory use of YIELD in 3.0. Refer to https://confluence.nebula-graph.io/pages/viewpage.action?pageId=10723963 -->
+
 The `LOOKUP` statement traverses data based on indexes. You can use `LOOKUP` for the following purposes:
 
 - Search for the specific data based on conditions defined by the `WHERE` clause.
@@ -35,19 +37,20 @@ Before using the `LOOKUP` statement, make sure that at least one index is create
 ```ngql
 LOOKUP ON {<vertex_tag> | <edge_type>} 
 [WHERE <expression> [AND <expression> ...]] 
-[YIELD <return_list>];
+[YIELD <return_list> [AS <alias>]];
 
 <return_list>
     <prop_name> [AS <col_alias>] [, <prop_name> [AS <prop_alias>] ...];
 ```
 
 - `WHERE <expression>`: filters data with specified conditions. Both `AND` and `OR` are supported between different expressions. For more information, see [WHERE](../8.clauses-and-options/where.md).
 
-- `YIELD <return_list>`: specifies the results to be returned and the format of the results.
+- `YIELD`: Define the output to be returned.
+
+  - When you `LOOKUP` a Tag, the defined properties and `VertexID` are returned. If there is no `YIELD` clause, `VertexID` is returned.
+  - When you `LOOKUP` an Edge type, the defined properties, `SrcVertexID`, `DstVertexID`, and `rank` are returned. If there is no `YIELD` clause, `SrcVertexID`, `DstVertexID`, and `rank` are returned.
 
-- If there is a `WHERE` clause but no `YIELD` clause:
-  - The Vertex ID is returned when you `LOOKUP` a tag.
-  - The source vertex ID, destination vertex ID, and rank of the edge are returned when `LOOKUP` an edge type.
+- `AS`: Set an alias.
 
 ## Limitations of using `WHERE` in `LOOKUP`
 
@@ -83,12 +86,12 @@ nebula> LOOKUP ON player \
 
 nebula> LOOKUP ON player \
         WHERE player.name == "Tony Parker" \
-        YIELD player.name, player.age;
-+-------------+---------------+------------+
-| VertexID    | player.name   | player.age |
-+-------------+---------------+------------+
-| "player101" | "Tony Parker" | 36         |
-+-------------+---------------+------------+
+        YIELD player.name AS name, player.age AS age;
++-------------+---------------+-----+
+| VertexID    | name          | age |
++-------------+---------------+-----+
+| "player101" | "Tony Parker" | 36  |
++-------------+---------------+-----+
 
 nebula> LOOKUP ON player \
         WHERE player.age  > 45;
@@ -208,7 +211,7 @@ For example, if there is a `player` tag with a `name` property and an `age` prop
 
     nebula> LOOKUP ON player;
     +-------------+
-    | _vid        |
+    |  VertexID   |
     +-------------+
     | "player100" |
     +-------------+
@@ -237,7 +240,7 @@ For example, if there is a `player` tag with a `name` property and an `age` prop
 
     nebula)> LOOKUP ON like;
     +-------------+----------+-------------+
-    | _src        | _ranking | _dst        |
+    | VertexID    | DstVID   | _dst        |
     +-------------+----------+-------------+
     | "player100" | 0        | "player101" |
     +-------------+----------+-------------+