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> {STEP|STEPS}] FROM {<vid>, <vid>...}
[{IN | OUT | BOTH} <edge_type>, <edge_type>...]
[WHERE <expression> [AND <expression> ...]]
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。

WHERE：指定遍历的过滤条件，可以结合布尔运算符 AND 使用。

YIELD：定义需要返回的输出。可以仅返回点或边。必须设置别名。

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。

WHERE 语句限制¶

在GET SUBGRAPH语句中使用WHERE子句，注意以下限制：

仅支持AND运算符。
仅支持过滤目的点，点的格式为$$.tagName.propName。
支持过滤边，边的格式为edge_type.propName。
支持数学函数、聚合函数、字符串函数、日期时间函数、列表函数中的通用函数和类型转化函数。
不支持聚合函数、Schema 相关函数、条件表达式函数、谓词函数、geo 函数和自定义函数，列表函数中除通用函数以外的函数。

示例¶

以下面的示例图进行演示。

A sample graph for GET SUBGRAPH

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。

GET SUBGRAPH FROM "player101"

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。

GET SUBGRAPH FROM "101" OUT serve

查询从点player101开始、0~2 跳、follow类型边degree大于 90，年龄大于 30 的子图，同时展示边的属性。

nebula> GET SUBGRAPH WITH PROP 2 STEPS FROM "player101" \
    WHERE follow.degree > 90 AND $$.player.age > 30 \
    YIELD VERTICES AS nodes, EDGES AS relationships;
+-------------------------------------------------------+------------------------------------------------------+
| nodes                                                 | relationships                                        |
+-------------------------------------------------------+------------------------------------------------------+
| [("player101" :player{age: 36, name: "Tony Parker"})] | [[:follow "player101"->"player100" @0 {degree: 95}]] |
| [("player100" :player{age: 42, name: "Tim Duncan"})]  | []                                                   |
+-------------------------------------------------------+------------------------------------------------------+

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。

FAQ

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 {}]]                                           |
+----------------------------------------------------+--------------------------------------------------------------------------------------+

最后更新: September 4, 2023