GET SUBGRAPH¶

The GET SUBGRAPH statement retrieves information of vertices and edges reachable from the source vertices of the specified edge types and returns information of the subgraph.

Syntax¶

GET SUBGRAPH [WITH PROP] [<step_count> STEPS] FROM {<vid>, <vid>...}
[IN <edge_type>, <edge_type>...]
[OUT <edge_type>, <edge_type>...]
[BOTH <edge_type>, <edge_type>...];

• WITH PROP shows the properties. If not specified, the properties will be hidden.

• step_count specifies the number of hops from the source vertices and returns the subgraph from 0 to step_count hops. It must be a non-negative integer. Its default value is 1.

• vid specifies the vertex IDs.

• edge_type specifies the edge type. You can use IN, OUT, and BOTH to specify the traversal direction of the edge type. The default is BOTH.

Examples¶

The following graph is used as the sample.

• This example goes one step from the vertex player100 over all edge types and gets the subgraph.

  nebula> GET SUBGRAPH 1 STEPS FROM "player100";
  +-------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+
  | _vertices                                                               | _edges                                                                                                                      |
  +-------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+
  | [("player100" :player{})]                                               | [[:serve "player100"->"team200" @0 {}], [:follow "player100"->"player101" @0 {}], [:follow "player100"->"player102" @0 {}]] |
  +-------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+
  | [("team200" :team{}), ("player101" :player{}), ("player102" :player{})] | [[:follow "player102"->"player101" @0 {}]]                                                                                  |
  +-------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+
  

  The returned subgraph is as follows.

  

• This example goes one step from the vertex player100 over incoming follow edges and gets the subgraph.

  nebula> GET SUBGRAPH 1 STEPS FROM "player100" IN follow;
  +---------------------------+--------+
  | _vertices                 | _edges |
  +---------------------------+--------+
  | [("player100" :player{})] | []     |     
  +---------------------------+--------+
  | []                        | []     |
  +---------------------------+--------+
  

  There is no incoming follow edge to player100, so no vertex or edge is returned.

• This example goes one step from the vertex player100 over outgoing serve edges, gets the subgraph, and shows the property of the edge.

  nebula> GET SUBGRAPH WITH PROP 1 STEPS FROM "player100" OUT serve;
  +------------------------------------------------------+-------------------------------------------------------------------------+
  | _vertices                                            | _edges                                                                  |
  +------------------------------------------------------+-------------------------------------------------------------------------+
  | [("player100" :player{age: 42, name: "Tim Duncan"})] | [[:serve "player100"->"team200" @0 {end_year: 2016, start_year: 1997}]] |
  +------------------------------------------------------+-------------------------------------------------------------------------+
  | [("team200" :team{name: "Warriors"})]                | []                                                                      |
  +------------------------------------------------------+-------------------------------------------------------------------------+
  

  The returned subgraph is as follows.

FAQ¶

Why is the number of hops in the returned result greater than step_count?¶

To show the completeness of the subgraph, an additional hop is made on all vertices that meet the conditions. The following graph is used as the sample.

• The returned paths of GET SUBGRAPH 1 STEPS FROM "A"; are A->B, B->A, and A->C. To show the completeness of the subgraph, an additional hop is made on all vertices that meet the conditions, namely B->C.

• The returned path of GET SUBGRAPH 1 STEPS FROM "A" IN follow; is B->A. To show the completeness of the subgraph, an additional hop is made on all vertices that meet the conditions, namely A->B.

If you only query paths or vertices that meet the conditions, we suggest you use MATCH or GO. The example is as follows.

nebula> match p= (v:player) -- (v2) where id(v)=="A" return p;

nebula> go 1 steps from "A" over follow;

Why is the number of hops in the returned result lower than step_count?¶

The query stops when there is not enough subgraph data and will not return the null value.

nebula> GET SUBGRAPH 100 STEPS FROM "player141" OUT follow;
+-------------------------------------------------------+--------------------------------------------+
| _vertices                                             | _edges                                     |
+-------------------------------------------------------+--------------------------------------------+
| [("player141" :player{age: 43, name: "Ray Allen"})]   | [[:follow "player141"->"player124" @0 {}]] |
+-------------------------------------------------------+--------------------------------------------+
| [("player124" :player{age: 33, name: "Rajon Rondo"})] | [[:follow "player124"->"player141" @0 {}]] |
+-------------------------------------------------------+--------------------------------------------+