Document lower bound restriction for shortestPath() and allShortestPath() functions #1146
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JPryce-Aklundh
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As this is a rule, it should get a mention in the Rules section. It could be kept to a minimum e.g.
Then add another example under Not allowed e.g. |
…only have a lower bound of 0 or 1 for its variable length pattern
…o the rules section
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blouerat
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Thanks for the documentation updates. The preview documentation has now been torn down - reopening this PR will republish it. |
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…th() functions (#1146) Document that the shortestPath() and allShortestPath() functions can only have a lower bound of 0 or 1 for its variable length pattern. This is not allowed: ` MATCH p=shortestPath((a:A)-[:R*2..]->(b:B)) RETURN 1` A lower bound can be specified using a filter, but might lead to executing a possibly very slow fallback plan. ` MATCH p=shortestPath((a:A)-[:R*]->(b:B)) WHERE length(p)>2 RETURN 1` The possibly very slow fallback plan is this part: ``` | | +Top | 3 | anon_1 ASC LIMIT 1 | 1 | In Pipeline 6 | | | | +----+-------------------------------------------------------+----------------+---------------------+ | | +Projection | 4 | length(p) AS anon_1 | 1 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Filter | 5 | length(p) > $autoint_0 | 1 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Projection | 6 | (a)-[anon_0*]->(b) AS p | 4 | | | | | +----+-------------------------------------------------------+----------------+ | | | +VarLengthExpand(Into) | 7 | (a)-[anon_0:R*]->(b) | 4 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Argument | 8 | a, b | 100 | Fused in Pipeline 5 | | | +----+-------------------------------------------------------+----------------+---------------------+ ``` Within this query plan: ``` +--------------------------+----+-------------------------------------------------------+----------------+---------------------+ | Operator | Id | Details | Estimated Rows | Pipeline | +--------------------------+----+-------------------------------------------------------+----------------+---------------------+ | +ProduceResults | 0 | `1` | 30 | | | | +----+-------------------------------------------------------+----------------+ | | +Projection | 1 | $autoint_1 AS `1` | 30 | | | | +----+-------------------------------------------------------+----------------+ | | +AntiConditionalApply | 2 | | 30 | Fused in Pipeline 7 | | |\ +----+-------------------------------------------------------+----------------+---------------------+ | | +Top | 3 | anon_1 ASC LIMIT 1 | 1 | In Pipeline 6 | | | | +----+-------------------------------------------------------+----------------+---------------------+ | | +Projection | 4 | length(p) AS anon_1 | 1 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Filter | 5 | length(p) > $autoint_0 | 1 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Projection | 6 | (a)-[anon_0*]->(b) AS p | 4 | | | | | +----+-------------------------------------------------------+----------------+ | | | +VarLengthExpand(Into) | 7 | (a)-[anon_0:R*]->(b) | 4 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Argument | 8 | a, b | 100 | Fused in Pipeline 5 | | | +----+-------------------------------------------------------+----------------+---------------------+ | +Apply | 9 | | 100 | | | |\ +----+-------------------------------------------------------+----------------+---------------------+ | | +Optional | 10 | a, b | 100 | In Pipeline 4 | | | | +----+-------------------------------------------------------+----------------+---------------------+ | | +ShortestPath | 11 | p = (a)-[anon_0:R*]->(b) WHERE length(p) > $autoint_0 | 30 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Argument | 12 | a, b | 100 | Fused in Pipeline 3 | | | +----+-------------------------------------------------------+----------------+---------------------+ | +CartesianProduct | 13 | | 100 | In Pipeline 2 | | |\ +----+-------------------------------------------------------+----------------+---------------------+ | | +NodeByLabelScan | 14 | b:B | 10 | In Pipeline 1 | | | +----+-------------------------------------------------------+----------------+---------------------+ | +NodeByLabelScan | 15 | a:A | 10 | In Pipeline 0 | +--------------------------+----+-------------------------------------------------------+----------------+---------------------+ ``` Better is to use the keyword-based SHORTEST. `MATCH p = SHORTEST 1 (a:A)-[:R]->{2,}(b:B) RETURN 1` --------- Co-authored-by: Jens Pryce-Åklundh <[email protected]>
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…th() functions (#1146) Document that the shortestPath() and allShortestPath() functions can only have a lower bound of 0 or 1 for its variable length pattern. This is not allowed: ` MATCH p=shortestPath((a:A)-[:R*2..]->(b:B)) RETURN 1` A lower bound can be specified using a filter, but might lead to executing a possibly very slow fallback plan. ` MATCH p=shortestPath((a:A)-[:R*]->(b:B)) WHERE length(p)>2 RETURN 1` The possibly very slow fallback plan is this part: ``` | | +Top | 3 | anon_1 ASC LIMIT 1 | 1 | In Pipeline 6 | | | | +----+-------------------------------------------------------+----------------+---------------------+ | | +Projection | 4 | length(p) AS anon_1 | 1 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Filter | 5 | length(p) > $autoint_0 | 1 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Projection | 6 | (a)-[anon_0*]->(b) AS p | 4 | | | | | +----+-------------------------------------------------------+----------------+ | | | +VarLengthExpand(Into) | 7 | (a)-[anon_0:R*]->(b) | 4 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Argument | 8 | a, b | 100 | Fused in Pipeline 5 | | | +----+-------------------------------------------------------+----------------+---------------------+ ``` Within this query plan: ``` +--------------------------+----+-------------------------------------------------------+----------------+---------------------+ | Operator | Id | Details | Estimated Rows | Pipeline | +--------------------------+----+-------------------------------------------------------+----------------+---------------------+ | +ProduceResults | 0 | `1` | 30 | | | | +----+-------------------------------------------------------+----------------+ | | +Projection | 1 | $autoint_1 AS `1` | 30 | | | | +----+-------------------------------------------------------+----------------+ | | +AntiConditionalApply | 2 | | 30 | Fused in Pipeline 7 | | |\ +----+-------------------------------------------------------+----------------+---------------------+ | | +Top | 3 | anon_1 ASC LIMIT 1 | 1 | In Pipeline 6 | | | | +----+-------------------------------------------------------+----------------+---------------------+ | | +Projection | 4 | length(p) AS anon_1 | 1 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Filter | 5 | length(p) > $autoint_0 | 1 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Projection | 6 | (a)-[anon_0*]->(b) AS p | 4 | | | | | +----+-------------------------------------------------------+----------------+ | | | +VarLengthExpand(Into) | 7 | (a)-[anon_0:R*]->(b) | 4 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Argument | 8 | a, b | 100 | Fused in Pipeline 5 | | | +----+-------------------------------------------------------+----------------+---------------------+ | +Apply | 9 | | 100 | | | |\ +----+-------------------------------------------------------+----------------+---------------------+ | | +Optional | 10 | a, b | 100 | In Pipeline 4 | | | | +----+-------------------------------------------------------+----------------+---------------------+ | | +ShortestPath | 11 | p = (a)-[anon_0:R*]->(b) WHERE length(p) > $autoint_0 | 30 | | | | | +----+-------------------------------------------------------+----------------+ | | | +Argument | 12 | a, b | 100 | Fused in Pipeline 3 | | | +----+-------------------------------------------------------+----------------+---------------------+ | +CartesianProduct | 13 | | 100 | In Pipeline 2 | | |\ +----+-------------------------------------------------------+----------------+---------------------+ | | +NodeByLabelScan | 14 | b:B | 10 | In Pipeline 1 | | | +----+-------------------------------------------------------+----------------+---------------------+ | +NodeByLabelScan | 15 | a:A | 10 | In Pipeline 0 | +--------------------------+----+-------------------------------------------------------+----------------+---------------------+ ``` Better is to use the keyword-based SHORTEST. `MATCH p = SHORTEST 1 (a:A)-[:R]->{2,}(b:B) RETURN 1` --------- Co-authored-by: Jens Pryce-Åklundh <[email protected]>
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Document that the shortestPath() and allShortestPath() functions can only have a lower bound of 0 or 1 for its variable length pattern.
This is not allowed:
MATCH p=shortestPath((a:A)-[:R*2..]->(b:B)) RETURN 1A lower bound can be specified using a filter, but might lead to executing a possibly very slow fallback plan.
MATCH p=shortestPath((a:A)-[:R*]->(b:B)) WHERE length(p)>2 RETURN 1The possibly very slow fallback plan is this part:
Within this query plan:
Better is to use the keyword-based SHORTEST.
MATCH p = SHORTEST 1 (a:A)-[:R]->{2,}(b:B) RETURN 1