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FETCH

FETCH可以获取指定点或边的属性值。

openCypher兼容性

本文操作仅适用于原生nGQL。

获取点的属性值

语法

FETCH PROP ON {<tag_name>[, tag_name ...] | *} 
<vid> [, vid ...] 
[YIELD <output>]
参数 说明
tag_name Tag名称。
* 表示当前图空间中的所有Tag。
vid 点ID。
output 指定要返回的信息。详情请参见YIELD。如果没有YIELD子句,将返回所有匹配的信息。

基于Tag获取点的属性值

FETCH语句中指定Tag获取对应点的属性值。

nebula> FETCH PROP ON player "player100";
+----------------------------------------------------+
| vertices_                                          |
+----------------------------------------------------+
| ("player100" :player{age: 42, name: "Tim Duncan"}) |
+----------------------------------------------------+

获取点的指定属性值

使用YIELD子句指定返回的属性。

nebula> FETCH PROP ON player "player100" \
        YIELD player.name;
+-------------+--------------+
| VertexID    | player.name  |
+-------------+--------------+
| "player100" | "Tim Duncan" |
+-------------+--------------+

获取多个点的属性值

指定多个点ID获取多个点的属性值,点之间用英文逗号(,)分隔。

nebula> FETCH PROP ON player "player101", "player102", "player103";
+-----------------------------------------------------------+
| vertices_                                                 |
+-----------------------------------------------------------+
| ("player101" :player{age: 36, name: "Tony Parker"})       |
+-----------------------------------------------------------+
| ("player102" :player{age: 33, name: "LaMarcus Aldridge"}) |
+-----------------------------------------------------------+
| ("player103" :player{age: 32, name: "Rudy Gay"})          |
+-----------------------------------------------------------+

基于多个Tag获取点的属性值

FETCH语句中指定多个Tag获取属性值。Tag之间用英文逗号(,)分隔。

# 创建新Tag t1。
nebula> CREATE TAG t1(a string, b int);

# 为点player100添加Tag t1。
nebula> INSERT VERTEX t1(a, b) VALUE "player100":("Hello", 100);

# 基于Tag player和t1获取点player100上的属性值。
nebula> FETCH PROP ON player, t1 "player100";
+----------------------------------------------------------------------------+
| vertices_                                                                  |
+----------------------------------------------------------------------------+
| ("player100" :t1{a: "Hello", b: 100} :player{age: 42, name: "Tim Duncan"}) |
+----------------------------------------------------------------------------+

用户可以在FETCH语句中组合多个Tag和多个点。

nebula> FETCH PROP ON player, t1 "player100", "player103";
+----------------------------------------------------------------------------+
| vertices_                                                                  |
+----------------------------------------------------------------------------+
| ("player100" :t1{a: "Hello", b: 100} :player{age: 42, name: "Tim Duncan"}) |
+----------------------------------------------------------------------------+
| ("player103" :player{age: 32, name: "Rudy Gay"})                           |
+----------------------------------------------------------------------------+

在所有标签中获取点的属性值

FETCH语句中使用*获取当前图空间所有标签里,点的属性值。

nebula> FETCH PROP ON * "player100", "player106", "team200";
+----------------------------------------------------------------------------+
| vertices_                                                                  |
+----------------------------------------------------------------------------+
| ("player106" :player{age: 25, name: "Kyle Anderson"})                      |
+----------------------------------------------------------------------------+
| ("team200" :team{name: "Warriors"})                                        |
+----------------------------------------------------------------------------+
| ("player100" :t1{a: "Hello", b: 100} :player{age: 42, name: "Tim Duncan"}) |
+----------------------------------------------------------------------------+

获取边的属性值

语法

FETCH PROP ON <edge_type> <src_vid> -> <dst_vid>[@<rank>] [, <src_vid> -> <dst_vid> ...]
[YIELD <output>]
参数 说明
edge_type Edge type名称。
src_vid 起始点ID,表示边的起点。
dst_vid 目的点ID,表示边的终点。
rank 边的rank。可选参数,默认值为0。起始点、目的点、Edge type和rank可以唯一确定一条边。
output 指定要返回的信息。详情请参见YIELD。如果没有YIELD子句,将返回所有匹配的信息。

获取边的所有属性值

# 获取连接player100和team204的边serve的所有属性值。
nebula> FETCH PROP ON serve "player100" -> "team204";
+-----------------------------------------------------------------------+
| edges_                                                                |
+-----------------------------------------------------------------------+
| [:serve "player100"->"team204" @0 {end_year: 2016, start_year: 1997}] |
+-----------------------------------------------------------------------+

获取边的指定属性值

使用YIELD子句指定返回的属性。

nebula> FETCH PROP ON serve "player100" -> "team204"    \
        YIELD serve.start_year;
+-------------+------------+-------------+------------------+
| serve._src  | serve._dst | serve._rank | serve.start_year |
+-------------+------------+-------------+------------------+
| "player100" | "team204"  | 0           | 1997             |
+-------------+------------+-------------+------------------+

获取多条边的属性值

指定多个边模式(<src_vid> -> <dst_vid>[@<rank>])获取多个边的属性值。模式之间用英文逗号(,)分隔。

nebula> FETCH PROP ON serve "player100" -> "team204", "player133" -> "team202";
+-----------------------------------------------------------------------+
| edges_                                                                |
+-----------------------------------------------------------------------+
| [:serve "player100"->"team204" @0 {end_year: 2016, start_year: 1997}] |
+-----------------------------------------------------------------------+
| [:serve "player133"->"team202" @0 {end_year: 2011, start_year: 2002}] |
+-----------------------------------------------------------------------+

基于rank获取属性值

如果有多条边,起始点、目的点和Edge type都相同,可以通过指定rank获取正确的边属性值。

# 插入不同属性值、不同rank的边。
nebula> insert edge serve(start_year,end_year) \
        values "player100"->"team204"@1:(1998, 2017);

nebula> insert edge serve(start_year,end_year) \
        values "player100"->"team204"@2:(1990, 2018);

# 默认返回rank为0的边。
nebula> FETCH PROP ON serve "player100" -> "team204";
+-----------------------------------------------------------------------+
| edges_                                                                |
+-----------------------------------------------------------------------+
| [:serve "player100"->"team204" @0 {end_year: 2016, start_year: 1997}] |
+-----------------------------------------------------------------------+

# 要获取rank不为0的边,请在FETCH语句中设置rank。
nebula> FETCH PROP ON serve "player100" -> "team204"@1;
+-----------------------------------------------------------------------+
| edges_                                                                |
+-----------------------------------------------------------------------+
| [:serve "player100"->"team204" @1 {end_year: 2017, start_year: 1998}] |
+-----------------------------------------------------------------------+

复合语句中使用FETCH

FETCH与原生nGQL结合使用是一种常见的方式,例如和GO一起。

# 返回从点player101开始的follow边的degree值。
nebula> GO FROM "player101" OVER follow \
        YIELD follow._src AS s, follow._dst AS d \
        | FETCH PROP ON follow $-.s -> $-.d \
        YIELD follow.degree;
+-------------+-------------+--------------+---------------+
| follow._src | follow._dst | follow._rank | follow.degree |
+-------------+-------------+--------------+---------------+
| "player101" | "player100" | 0            | 95            |
+-------------+-------------+--------------+---------------+
| "player101" | "player102" | 0            | 90            |
+-------------+-------------+--------------+---------------+
| "player101" | "player125" | 0            | 95            |
+-------------+-------------+--------------+---------------+

用户也可以通过自定义变量构建类似的查询。

nebula> $var = GO FROM "player101" OVER follow \
        YIELD follow._src AS s, follow._dst AS d; \
        FETCH PROP ON follow $var.s -> $var.d \
        YIELD follow.degree;
+-------------+-------------+--------------+---------------+
| follow._src | follow._dst | follow._rank | follow.degree |
+-------------+-------------+--------------+---------------+
| "player101" | "player100" | 0            | 95            |
+-------------+-------------+--------------+---------------+
| "player101" | "player102" | 0            | 90            |
+-------------+-------------+--------------+---------------+
| "player101" | "player125" | 0            | 95            |
+-------------+-------------+--------------+---------------+

更多复合语句的详情,请参见复合查询(子句结构)


最后更新: July 26, 2021
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