GET SUBGRAPH

GET SUBGRAPH语句查询并返回一个通过从指定点出发对图进行游走而生成的子图。在GET SUBGRAPH语句中，用户可以指定游走的步数以及游走所经过的边的类型或方向。

语法

GET SUBGRAPH [WITH PROP] [<step_count> STEPS] FROM {<vid>, <vid>...}
[{IN | OUT | BOTH} <edge_type>, <edge_type>...]
YIELD [VERTICES AS <vertex_alias>] [, EDGES AS <edge_alias>];

• WITH PROP：展示属性。不添加本参数则隐藏属性。

• step_count：指定从起始点开始的跳数，返回从 0 到step_count跳的子图。必须是非负整数。默认值为 1。

• vid：指定起始点 ID。

• edge_type：指定 Edge type。可以用IN、OUT和BOTH来指定起始点上该 Edge type 的方向。默认为BOTH。

• YIELD：定义需要返回的输出。可以仅返回点或边。必须设置别名。

Caution

GET SUBGRAPH语句不支持使用WHERE子句。

Note

GET SUBGRAPH语句检索的路径类型为trail，即检索的路径只有点可以重复，边不可以重复。详情请参见路径。

示例

以下面的示例图进行演示。

插入测试数据：

nebula> CREATE SPACE IF NOT EXISTS subgraph(partition_num=15, replica_factor=1, vid_type=fixed_string(30));
nebula> USE subgraph;
nebula> CREATE TAG IF NOT EXISTS player(name string, age int);
nebula> CREATE TAG IF NOT EXISTS team(name string);
nebula> CREATE EDGE IF NOT EXISTS follow(degree int);
nebula> CREATE EDGE IF NOT EXISTS serve(start_year int, end_year int);
nebula> INSERT VERTEX player(name, age) VALUES "player100":("Tim Duncan", 42);
nebula> INSERT VERTEX player(name, age) VALUES "player101":("Tony Parker", 36);
nebula> INSERT VERTEX player(name, age) VALUES "player102":("LaMarcus Aldridge", 33);
nebula> INSERT VERTEX team(name) VALUES "team203":("Trail Blazers"), "team204":("Spurs");
nebula> INSERT EDGE follow(degree) VALUES "player101" -> "player100":(95);
nebula> INSERT EDGE follow(degree) VALUES "player101" -> "player102":(90);
nebula> INSERT EDGE follow(degree) VALUES "player102" -> "player100":(75);
nebula> INSERT EDGE serve(start_year, end_year) VALUES "player101" -> "team204":(1999, 2018),"player102" -> "team203":(2006,  2015);

• 查询从点player101开始、0~1 跳、所有 Edge type 的子图。

  nebula> GET SUBGRAPH 1 STEPS FROM "player101" YIELD VERTICES AS nodes, EDGES AS relationships;
  +-------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+
  | nodes                                                                   | relationships                                                                                                               |
  +-------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+
  | [("player101" :player{})]                                               | [[:serve "player101"->"team204" @0 {}], [:follow "player101"->"player100" @0 {}], [:follow "player101"->"player102" @0 {}]] |
  | [("team204" :team{}), ("player100" :player{}), ("player102" :player{})] | [[:follow "player102"->"player100" @0 {}]]                                                                                  |
  +-------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+
  

  返回的子图如下。

  

• 查询从点player101开始、0~1 跳、follow类型的入边的子图。

  nebula> GET SUBGRAPH 1 STEPS FROM "player101" IN follow YIELD VERTICES AS nodes, EDGES AS relationships;
  +---------------------------+---------------+
  | nodes                     | relationships |
  +---------------------------+---------------+
  | [("player101" :player{})] | []            |
  | []                        | []            |
  +---------------------------+---------------+
  

  因为player101没有follow类型的入边。所以仅返回点player101。

• 查询从点player101开始、0~1 跳、serve类型的出边的子图，同时展示边的属性。

  nebula> GET SUBGRAPH WITH PROP 1 STEPS FROM "player101" OUT serve YIELD VERTICES AS nodes, EDGES AS relationships;
  +-------------------------------------------------------+-------------------------------------------------------------------------+
  | nodes                                                 | relationships                                                           |
  +-------------------------------------------------------+-------------------------------------------------------------------------+
  | [("player101" :player{age: 36, name: "Tony Parker"})] | [[:serve "player101"->"team204" @0 {end_year: 2018, start_year: 1999}]] |
  | [("team204" :team{name: "Spurs"})]                    | []                                                                      |
  +-------------------------------------------------------+-------------------------------------------------------------------------+
  

  返回的子图如下。

  

FAQ

为什么返回结果中会出现超出step_count跳数之外的关系？

为了展示子图的完整性，会在满足条件的所有点上额外查询一跳。例如下图。

• 用GET SUBGRAPH 1 STEPS FROM "A";查询的满足结果的路径是A->B、B->A和A->C，为了子图的完整性，会在满足结果的点上额外查询一跳，即B->C。

• 用GET SUBGRAPH 1 STEPS FROM "A" IN follow;查询的满足结果的路径是B->A，在满足结果的点上额外查询一跳，即A->B。

如果只是查询满足条件的路径或点，建议使用 MATCH 或 GO 语句。例如：

nebula> MATCH p= (v:player) -- (v2) WHERE id(v)=="A" RETURN p;

nebula> GO 1 STEPS FROM "A" OVER follow YIELD src(edge),dst(edge);

为什么返回结果中会出现低于step_count跳数的关系？

查询到没有多余子图数据时会停止查询，且不会返回空值。

nebula> GET SUBGRAPH 100 STEPS FROM "player101" OUT follow YIELD VERTICES AS nodes, EDGES AS relationships;
+----------------------------------------------------+--------------------------------------------------------------------------------------+
| nodes                                              | relationships                                                                        |
+----------------------------------------------------+--------------------------------------------------------------------------------------+
| [("player101" :player{})]                          | [[:follow "player101"->"player100" @0 {}], [:follow "player101"->"player102" @0 {}]] |
| [("player100" :player{}), ("player102" :player{})] | [[:follow "player102"->"player100" @0 {}]]                                           |
+----------------------------------------------------+--------------------------------------------------------------------------------------+

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最后更新: February 3, 2023