Nebula Graph数据库的简单查询

2023-10-08 17:44:58

数据来源

这里使用的数据数据是使用 Nebula Console 创建的测试数据

nebula> :play nba

https://docs.nebula-graph.com.cn/2.6.1/2.quick-start/3.connect-to-nebula-graph/#_3

数据结构

> show tags
+------------+
| Name       |
+------------+
| "bachelor" |
| "player"   |
| "team"     |
+------------+
Got 3 rows (time spent 995/3049 us)

show edges;
+------------+
| Name       |
+------------+
| "like"     |
| "serve"    |
| "teammate" |
+------------+
Got 3 rows (time spent 1105/3187 us)

show tag indexes;
+---------------------+----------+----------+
| Index Name          | By Tag   | Columns  |
+---------------------+----------+----------+
| "player_age_index"  | "player" | ["age"]  |
| "player_name_index" | "player" | ["name"] |
| "team_name_index"   | "team"   | ["name"] |
+---------------------+----------+----------+
Got 3 rows (time spent 1043/2790 us)

show edge indexes;
+-------------------+------------+----------------+
| Index Name        | By Edge    | Columns        |
+-------------------+------------+----------------+
| "like_index"      | "like"     | ["likeness"]   |
| "serve_index1"    | "serve"    | ["start_year"] |
| "serve_index2"    | "serve"    | ["end_year"]   |
| "teammate_index1" | "teammate" | ["start_year"] |
| "teammate_index2" | "teammate" | ["end_year"]   |
+-------------------+------------+----------------+
Got 5 rows (time spent 1586/3821 us)

常用查询语句

GO 语句

GO 语句可以根据指定的条件遍历数据库。GO语句从一个或多个点开始，沿着一条或多条边遍历，返回YIELD子句中指定的信息。

查询球员 VID "Tim Duncan" 关注 (like) 的其他球员。

go from "Tim Duncan" over like;
+-----------------+
| like._dst       |
+-----------------+
| "Manu Ginobili" |
| "Tony Parker"   |
+-----------------+
Got 2 rows (time spent 2062/4471 us)

查询球员 VID "Tim Duncan" 关注的球员，被关注球员年龄需大于 38 岁。返回其姓名和年龄，并取别名为 Teammate 和 Age。

 go from "Tim Duncan" over like \
                  -> where $$.player.age >= 38 \
                  -> yield $$.player.name as teammate, $$.player.age as age;
+-----------------+-----+
| teammate        | age |
+-----------------+-----+
| "Manu Ginobili" | 41  |
+-----------------+-----+
Got 1 rows (time spent 3056/6108 us)

说明：

YIELD 指定希望从查询中返回的结果。
$$ 表示边上的目的点。
\ 表示换行符。是命令行特有的。

查询球员 "Tim Duncan" 关注的球员所效力的球队。

使用管道(|) 来组合两个查询语句

> go from "Tim Duncan" over like yield like._dst as id |  \
                  -> go from $-.id over serve yield $$.team.name as Team, $^.player.name as Player;
+-----------+-----------------+
| Team      | Player          |
+-----------+-----------------+
| "Spurs"   | "Manu Ginobili" |
| "Hornets" | "Tony Parker"   |
| "Spurs"   | "Tony Parker"   |
+-----------+-----------------+
Got 3 rows (time spent 3635/7094 us)

说明：

球员 "Tim Duncan" 关注的球员 go from "Tim Duncan" over like yield like._dst as id
$^ 表示边的起始点。
| 表示管道。
$- 表示输入流。上一个查询的输出(id)作为下一个查询的输入($-.id)。

使用自定义的变量来组合两个查询语句

 $var = go from "Tim Duncan" over like yield like._dst as id ; \
                  -> go from $var.id over serve yield $$.team.name as Team, $^.player.name as Player;
+-----------+-----------------+
| Team      | Player          |
+-----------+-----------------+
| "Spurs"   | "Manu Ginobili" |
| "Hornets" | "Tony Parker"   |
| "Spurs"   | "Tony Parker"   |
+-----------+-----------------+
Got 3 rows (time spent 3822/7353 us)

当一条组合语句被整体提交给服务器后，该语句内的自定义变量就已结束生命周期。

LOOKUP 语句

LOOKUP 语句是基于索引的，和WHERE子句一起使用，查找符合特定条件的数据。

返回名称为 Tony Parker，标签为 player 的顶点。

 lookup on player where player.name == "Tony Parker" yield player.name,player.age;
+---------------+---------------+------------+
| VertexID      | player.name   | player.age |
+---------------+---------------+------------+
| "Tony Parker" | "Tony Parker" | 36         |
+---------------+---------------+------------+
Got 1 rows (time spent 2078/4748 us)

FETCH 语句

FETCH 语句可以获得点或边的属性。

如果要获取点的数据，则必须指定点的标签和点 VID；
如果要获取边数据，则必须指定边的类型、起始点 VID 和目标点 VID。

 FETCH PROP ON player "Tony Parker";
+-------------------------------------------------------+
| vertices_                                             |
+-------------------------------------------------------+
| ("Tony Parker" :player{age: 36, name: "Tony Parker"}) |
+-------------------------------------------------------+
Got 1 rows (time spent 1358/3745 us)



FETCH PROP ON serve "Tony Parker" -> "Spurs";
+-----------------------------------------------------------------------+
| edges_                                                                |
+-----------------------------------------------------------------------+
| [:serve "Tony Parker"->"Spurs" @0 {end_year: 2018, start_year: 1999}] |
+-----------------------------------------------------------------------+
Got 1 rows (time spent 2098/5039 us)

MATCH 语句

MATCH 语句是查询图数据最常用的，可以灵活的描述各种图模式，但是它依赖索引去匹配 Nebula Graph 中的数据模型，性能也还需要调优。

匹配点的属性的前提是 Tag 本身有对应属性的索引，否则，用户无法执行 MATCH 语句匹配该属性。

match (v:player) return v ;

 match (v:player{name:"Tim Duncan"}) return v ;
+-------------------------------------------------------------------------------------------------------------+
| v                                                                                                           |
+-------------------------------------------------------------------------------------------------------------+
| ("Tim Duncan" :bachelor{name: "Tim Duncan", speciality: "psychology"} :player{age: 42, name: "Tim Duncan"}) |
+-------------------------------------------------------------------------------------------------------------+
Got 1 rows (time spent 3920/7082 us)

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