Document LET
#1207
Document LET
#1207
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This PR includes documentation updates New pages: Updated pages: |
| @@ -178,6 +178,11 @@ For example, GQL’s graph reference values `CURRENT_GRAPH` and `CURRENT_PROPERT | |||
| | xref:clauses/filter.adoc[`FILTER`] | |||
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| | GQ09 | |||
| | `LET` statement | |||
| | xref:clauses/let.adoc[`LET`] | |||
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Just FYI: There is a caveat to this, since there is a sub-functionality which we do not support, cf. Appendix of the CIP. However, that is much in the detail and other implementation do not support that either. Additionally, I am trying to make this bit optional in the standard. Bottom line: I would not change anything here at this point, but we may want to in the future (e.g. when making it optional in the standard fails).
| m| xref::clauses/unwind.adoc[UNWIND ... [AS]] | ||
| | Expands a list into a sequence of rows. | ||
| m| xref::clauses/let.adoc[LET] | ||
| | Assigns expressions to variables. |
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More correct is that the results of expressions are assigned to that variables.
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Alternatively, you could say something like "defines additional variables" or "binds additional variables". Not sure I like these more. Just throwing out ideas.
| m| xref::clauses/filter.adoc[FILTER] | ||
| | Adds filters to queries. | ||
| label:new[Introduced in Neo4j 2025.03] |
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Didn't saw this on the FILTER review, but I think this FILTER is in the wrong section, since it does not project anything. Reading clauses is probably better.
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| `LET` binds expressions to variables. | ||
| For queries involving several chained expressions, it can be a more succinct and readable alternative to xref:clauses/with.adoc[`WITH`]. | ||
| Unlike `WITH`, `LET` cannot limit the scope of variables available to subsequent clauses. |
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| Unlike `WITH`, `LET` cannot limit the scope of variables available to subsequent clauses. | |
| Unlike `WITH`, `LET` does not remove variables from the scope for subsequent clauses. |
I feel this sound more positive ... "it does not limit" is somehow slightly negatively connotated for me, while "it does not remove" is somehow slightly negatively connotated for me. ... may that is just me.
| [[assigning-expressions-to-variables]] | ||
| == Assigning expressions to a variable | ||
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| Both `Let` and `WITH` can be used to assign variables to an expression: |
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| Both `Let` and `WITH` can be used to assign variables to an expression: | |
| Both `LET` and `WITH` can be used to assign variables to an expression: |
| * `LET` syntax: `LET <variable> = <expression>, <variable> = <expression>` | ||
| * `WITH` syntax: `WITH <expression> AS <variable>, <expression> AS <variable>` |
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This may make look like they do the same, which they do not. As explained at the top and in the next section ("Variables in scope: comparing LET and WITH"). So, I wonder if we need that here.
May we make this section just about LET and do not mention WITH at all. It is mentioned enough at the top and in the next section.
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| [[assigning-expressions-to-variables]] | ||
| == Assigning expressions to a variable |
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Cf. Comment on the index page. (Also the plural doesn't fit, because it is one expression per variable. That one expression may be evaluated to multiple values.)
Here is another proposal:
| == Assigning expressions to a variable | |
| == Assigning values to a variable |
| === Variables in scope | ||
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| `LET` and `WITH` behave differently in terms of what variables remain in scope for subsequent clauses. | ||
| Unlike `WITH`, `LET` cannot drop variables from the scope of subsequent clauses. |
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| Unlike `WITH`, `LET` cannot drop variables from the scope of subsequent clauses. | |
| Unlike `WITH`, `LET` does not drop variables from the scope of subsequent clauses. |
cf. above. I like this version with "drop" over my own suggestion from above.
Or more LET-oriented:
| Unlike `WITH`, `LET` cannot drop variables from the scope of subsequent clauses. | |
| `LET` does not drop variables from the scope of subsequent clauses, while `WITH` does. |
(or the other way around).
We should pay attention that the page works for someone who is not familiar with WITH.
| [[chaining-expressions]] | ||
| === Chaining expressions | ||
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| The fact that `LET` does not drop variables means that it can be used to chain expressions in a clear and concise manner, where variables bound in one `LET` clause can be referenced by subsequent clauses. |
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| MATCH (c:Customer)-[:BUYS]->(p:Product) | ||
| WITH DISTINCT c, sum(p.price) AS totalSpent | ||
| LET fullName = c.firstName + ' ' + c.lastName, |
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| LET fullName = c.firstName + ' ' + c.lastName, | |
| LET fullName = c.firstName + ' ' + c.lastName |
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