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feat(clickhouse): Add support for APPLY query modifier #4141

Merged
merged 4 commits into from
Sep 23, 2024
Merged

feat(clickhouse): Add support for APPLY query modifier #4141

merged 4 commits into from
Sep 23, 2024

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VaggelisD
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Fixes #4139

Clickhouse supports the APPLY query modifier:

SELECT <expr> APPLY( <func> ) FROM [db.]table_name

Although apply is still a valid alias, we shouldn't parse it as such if it's accompanied by an L_PAREN as is the case here, thus the overriden _parse_alias() in Clickhouse:

clickhouse> select 1 apply;

   ┌─apply─┐
1. │     1 │
   └───────┘

clickhouse> with t as (Select 1 as col) select COLUMNS('col') apply(sum) from t;

   ┌─sum(col)─┐
1. │        1 │
   └──────────┘

Note that APPLY can be chained, as is shown in the docs & relevant test case

Docs

Clickhouse APPLY modifier

@tobymao
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tobymao commented Sep 20, 2024

is this the right approach? should we treat this similarly to window functions?

@VaggelisD
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VaggelisD commented Sep 20, 2024 •
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@tobymao Clickhouse is a bit lax with the rules, the grammar etc so I struggled a bit to not break any functionality as with the apply alias vs modifier. Regarding window functions, which part would that be, reusing _parse_query_modifiers()?

Note that APPLY comes before the query's FROM so we must either parse it early on it's own (the approach here) or add it in QUERY_MODIFIER_PARSERS and call _parse_query_modifiers() in the place of my current while loop afaict.

tobymao
tobymao reviewed Sep 20, 2024
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sqlglot/parser.py Outdated Show resolved Hide resolved
@VaggelisD VaggelisD merged commit 3ec96ab into main Sep 23, 2024
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@VaggelisD VaggelisD deleted the vaggelisd/clickhouse_apply branch September 23, 2024 16:27
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@georgesittas georgesittas georgesittas approved these changes

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Clickhouse COLUMNS APPLY parsing error
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@VaggelisD @tobymao @georgesittas