Traces of lists Jzsef Marton Budapest University of Technology and - - PowerPoint PPT Presentation

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Mar 04, 2023 237 likes •301 views

Traces of lists Jzsef Marton Budapest University of Technology and Economics 2017-05-10, oCIM2@London Jzsef Marton - Traces of lists 1 CIR-2017-220 Specify order of list elements in list constructing functions collect( expr ) -

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2017-05-10, oCIM2@London József Marton - Traces of lists 1

Traces of lists

József Marton Budapest University of Technology and Economics

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2017-05-10, oCIM2@London József Marton - Traces of lists 2

Specify order of list elements in list constructing functions

collect( expr ) - aggregates expr into a list
rder of elements not specified, input ordering?? (if any) #165
what if collecting more lists with different ordering?

–

List comprehensions? #190, #202

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extend syntax

For the current syntax:

UNWIND range(1, 10) as i // 1st query step RETURN collect(i ORDER BY i ASC) AS l // 2nd query step

For CIP2017-04-13 syntax

UNWIND range(1, 10) as i // 1st query step RETURN collect OF i ORDER BY i ASC AS l // 2nd query step

CIR-2017-220

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2017-05-10, oCIM2@London József Marton - Traces of lists 3

Resultset ordering between query steps

Does ordering matter in subsequent query steps?

MATCH (n) WITH n O R D E R b y n . v a l u e OPTIONAL MATCH (n)-->(m) RETURN n, m

Another example for collecting list in #165
If it matters,

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pros: intuitive, currently() this is the way to set order for collect : see CIR-2017-220

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cons: poses difficulties() for parallel query evaluation : performance loss

CIR TODO

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2017-05-10, oCIM2@London József Marton - Traces of lists 4

OPTIONAL UNWIND

Given four persons and the languages they command

CREATE (:Demo {name: 'Alice', languages: ['en', 'de', 'gr'] }) , (:Demo {name: 'Bob', languages: ['en', 'de'] }) , (:Demo {name: 'Cecil', languages: [] }) , (:Demo {name: 'Dennis' })

CIR-2017-234

MATCH (n:Demo) UNWIND n.languages AS lang RETURN n.name, lang

╒════════╤══════╕ │"n.name"│"lang"│ ╞════════╪══════╡ │"Alice" │"en" │ ├────────┼──────┤ │"Alice" │"de" │ ├────────┼──────┤ │"Alice" │"gr" │ ├────────┼──────┤ │"Bob" │"en" │ ├────────┼──────┤ │"Bob" │"de" │ └────────┴──────┘ ╒════════╤══════╕ │"n.name"│"lang"│ ╞════════╪══════╡ │"Alice" │"en" │ ├────────┼──────┤ │"Alice" │"de" │ ├────────┼──────┤ │"Alice" │"gr" │ ├────────┼──────┤ │"Bob" │"en" │ ├────────┼──────┤ │"Bob" │"de" │ ├────────┼──────┤ │"Cecil" │NULL │ ├────────┼──────┤ To be decided --> │"Dennis"│NULL │ └────────┴──────┘

MATCH (n:Demo) OPTIONAL UNWIND n.languages AS lang RETURN n.name, lang

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2017-05-10, oCIM2@London József Marton - Traces of lists 5

That‘s all

1. Specify order of list elements in list constructing

functions

2. Resultset ordering between query steps
3. OPTIONAL UNWIND

Content presented here are a collection of current Cypher Improvement Requests (CIR), problems and ideas. They might change if/when they are built in the openCypher language.