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FETCH

The FETCH statement retrieves the properties of the specified vertices or edges.

OpenCypher Compatibility

This topic applies to native nGQL only.

Fetch vertex properties

Syntax

FETCH PROP ON {<tag_name>[, tag_name ...] | *}
<vid> [, vid ...]
YIELD <return_list> [AS <alias>];
Parameter Description
tag_name The name of the tag.
* Represents all the tags in the current graph space.
vid The vertex ID.
YIELD Define the output to be returned. For details, see YIELD.
AS Set an alias.

Fetch vertex properties by one tag

Specify a tag in the FETCH statement to fetch the vertex properties by that tag.

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

Fetch specific properties of a vertex

Use a YIELD clause to specify the properties to be returned.

nebula> FETCH PROP ON player "player100" \
        YIELD properties(vertex).name AS name;
+--------------+
| name         |
+--------------+
| "Tim Duncan" |
+--------------+

Fetch properties of multiple vertices

Specify multiple VIDs (vertex IDs) to fetch properties of multiple vertices. Separate the VIDs with commas.

nebula> FETCH PROP ON player "player101", "player102", "player103" YIELD properties(vertex);
+--------------------------------------+
| properties(VERTEX)                   |
+--------------------------------------+
| {age: 33, name: "LaMarcus Aldridge"} |
| {age: 40, name: "Tony Parker"}       |
| {age: 32, name: "Rudy Gay"}          |
+--------------------------------------+

Fetch vertex properties by multiple tags

Specify multiple tags in the FETCH statement to fetch the vertex properties by the tags. Separate the tags with commas.

# The following example creates a new tag t1.
nebula> CREATE TAG IF NOT EXISTS t1(a string, b int);

# The following example attaches t1 to the vertex "player100".
nebula> INSERT VERTEX t1(a, b) VALUES "player100":("Hello", 100);

# The following example fetches the properties of vertex "player100" by the tags player and t1.
nebula> FETCH PROP ON player, t1 "player100" YIELD vertex AS v;
+----------------------------------------------------------------------------+
| v                                                                          |
+----------------------------------------------------------------------------+
| ("player100" :player{age: 42, name: "Tim Duncan"} :t1{a: "Hello", b: 100}) |
+----------------------------------------------------------------------------+

You can combine multiple tags with multiple VIDs in a FETCH statement.

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

Fetch vertex properties by all tags

Set an asterisk symbol * to fetch properties by all tags in the current graph space.

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

Fetch edge properties

Syntax

FETCH PROP ON <edge_type> <src_vid> -> <dst_vid>[@<rank>] [, <src_vid> -> <dst_vid> ...]
YIELD <output>;
Parameter Description
edge_type The name of the edge type.
src_vid The VID of the source vertex. It specifies the start of an edge.
dst_vid The VID of the destination vertex. It specifies the end of an edge.
rank The rank of the edge. It is optional and defaults to 0. It distinguishes an edge from other edges with the same edge type, source vertex, destination vertex, and rank.
YIELD Define the output to be returned. For details, see YIELD.

Fetch all properties of an edge

The following statement fetches all the properties of the serve edge that connects vertex "player100" and vertex "team204".

nebula> FETCH PROP ON serve "player100" -> "team204" YIELD properties(edge);
+------------------------------------+
| properties(EDGE)                   |
+------------------------------------+
| {end_year: 2016, start_year: 1997} |
+------------------------------------+

Fetch specific properties of an edge

Use a YIELD clause to fetch specific properties of an edge.

nebula> FETCH PROP ON serve "player100" -> "team204"    \
        YIELD properties(edge).start_year;
+-----------------------------+
| properties(EDGE).start_year |
+-----------------------------+
| 1997                        |
+-----------------------------+

Fetch properties of multiple edges

Specify multiple edge patterns (<src_vid> -> <dst_vid>[@<rank>]) to fetch properties of multiple edges. Separate the edge patterns with commas.

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

Fetch properties based on edge rank

If there are multiple edges with the same edge type, source vertex, and destination vertex, you can specify the rank to fetch the properties on the correct edge.

# The following example inserts edges with different ranks and property values.
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);

# By default, the FETCH statement returns the edge whose rank is 0.
nebula> FETCH PROP ON serve "player100" -> "team204" YIELD edge AS e;
+-----------------------------------------------------------------------+
| e                                                                     |
+-----------------------------------------------------------------------+
| [:serve "player100"->"team204" @0 {end_year: 2016, start_year: 1997}] |
+-----------------------------------------------------------------------+

# To fetch on an edge whose rank is not 0, set its rank in the FETCH statement.
nebula> FETCH PROP ON serve "player100" -> "team204"@1 YIELD edge AS e;
+-----------------------------------------------------------------------+
| e                                                                     |
+-----------------------------------------------------------------------+
| [:serve "player100"->"team204" @1 {end_year: 2017, start_year: 1998}] |
+-----------------------------------------------------------------------+

Use FETCH in composite queries

A common way to use FETCH is to combine it with native nGQL such as GO.

The following statement returns the degree values of the follow edges that start from vertex "player101".

nebula> GO FROM "player101" OVER follow \
        YIELD src(edge) AS s, dst(edge) AS d \
        | FETCH PROP ON follow $-.s -> $-.d \
        YIELD properties(edge).degree;
+-------------------------+
| properties(EDGE).degree |
+-------------------------+
| 95                      |
| 90                      |
| 95                      |
+-------------------------+

Or you can use user-defined variables to construct similar queries.

nebula> $var = GO FROM "player101" OVER follow \
        YIELD src(edge) AS s, dst(edge) AS d; \
        FETCH PROP ON follow $var.s -> $var.d \
        YIELD properties(edge).degree;
+-------------------------+
| properties(EDGE).degree |
+-------------------------+
| 95                      |
| 90                      |
| 95                      |
+-------------------------+

For more information about composite queries, see Composite queries (clause structure).


Last update: September 16, 2022