#nebula-users
Title
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Sandeep
08/16/2022, 11:36 AMHi all. I'm trying to display all the nodes and edges using the following query
MATCH (m)-[e]->(n) RETURN m,n,e limit 10;
But I'm getting the following error:
Scan vertices or edges need to specify a limit number, or limit number can not push down
Can someone please clarify?
w
wey
08/16/2022, 11:51 AMDear Sandeep, welcome to the NebulaGraph community 🙂
Will come back to you seen, I am on a meeting now, you could have a look at index related doc/post first, I will come back with more explanation later after the meeting.
• https://docs.nebula-graph.io/3.2.0/3.ngql-guide/14.native-index-statements/
• https://www.siwei.io/en/nebula-index-explained/
s
Sandeep
08/16/2022, 12:06 PMHi @wey. Thanks for the quick reply and sharing the reference links. I'll check them out. (To provide more context on my query: I'm using Nebula studio and I need all the available nodes and edges to be displayed as connected graph representation)
w
wey
08/17/2022, 7:50 AMHi @Sandeep
Sorry for the late follow-up.
The Long version comes:
In NebulaGraph, `(m)-[e]->(n) RETURN m,n,e limit 10`was not allowed by complaining cannot be pushed down is due to we forbidden queries introducing full scan of data.
By full scan, I am referring to this pattern didn’t specify any vertex or edge types, thus the limit cannot be pushed down to the storage side when scanning data.
More specifically, in graphD, it will construct an execution plan to starting from scan of vertex or edge (or index is there is any), then get neighbors, etc…, the case without any tag/edge type cannot be efficiently pushdown (as nebulaGraph was designed schemaFul to enable high perf for large scale data).
Thus the mind module in NebulaGraph with Cypher to sample node/edges could be:
When no indexes were created(on tag or edge):
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match ()-[e:follow|:serve]->() return e limit 100 Copy code
match (v:player) return v limit 10when there is index on tag: player
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match (v:player)-[e:follow|:serve]->(v1) return v,e,v1To provide more context on my query: I’m using Nebula studio and I need all the available nodes and edges to be displayed as connected graph representationLet’s take an example of basketballplayer dataset • ref: https://docs.nebula-graph.io/3.2.0/3.ngql-guide/14.native-index-statements/1.create-native-index/ • ref: https://docs.nebula-graph.io/3.2.0/3.ngql-guide/14.native-index-statements/4.rebuild-native-index/
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CREATE TAG INDEX IF NOT EXISTS player_index_1 on player(name(10), age);
REBUILD TAG INDEX player_index_1;
SHOW TAG INDEX STATUS; Copy code
match (v:player)-[e:follow|:serve]->(v1) return v,e,v1s
Sandeep
08/30/2022, 10:59 PMHi @wey. Sorry for the late response. Thanks a lot for the detailed explanation.
❤️ 1
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