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GeezerVison is showing github.com — DuckDB: support list comprehensions by guizmaii · Pull Request #2798 · JSQLParser/JSqlParser

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@guizmaii

@guizmaii guizmaii commented Oct 13, 2026 •
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For DuckDB's list comprehensions (docs):

SELECT [x * 2 FOR x IN l IF x > 1], [x + i FOR x, i IN l] FROM t
  • New ListComprehension expression: element expression, one or two variables (element, 1-based index), list expression, optional IF condition.
  • A [ opens a comprehension only when FOR follows at its top level (isListComprehensionAhead(), one pass over the token chain; a 20,000-element array parses as fast as on master); every other [ is still an ArrayConstructor. [... FOR ...] was a syntax error in every dialect, so nothing that parsed before changes. SQL Server's [name] quoting is lexed before this and unaffected.
  • ExpressionVisitor.visit(ListComprehension) is a default method visiting the element, list and condition, so existing visitors keep compiling. The deparser, adapter, validator and TablesNamesFinder implement it (tables in a sub-select list are found).
  • checkGrammarAmbiguity: no conflicts. ./gradlew check: 10,120 tests, 0 failures.
  • DuckDB's own test suite (test/sql, 70,729 statements): 91 more parse, none less.

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@guizmaii
guizmaii marked this pull request as ready for review October 13, 2026 08:57
Copilot AI balanced review requested due to automatic review settings October 13, 2026 08:57
Copilot AI reviewed Oct 13, 2026

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@guizmaii guizmaii mentioned this pull request Oct 13, 2026
DuckDB: remaining syntax to support #2804
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@guizmaii
guizmaii force-pushed the duckdb-list-comprehension branch 3 times, most recently from 327524b to bb13af8 Compare October 13, 2026 21:48
guizmaii added 2 commits October 14, 2026 08:55
@guizmaii
DuckDB: support list comprehensions
63e3a8f 
`[x * 2 FOR x IN l IF x > 1]` and `[x + i FOR x, i IN l]` parse as the
new `ListComprehension`. A `[` opens one when a `FOR` follows at its top
level; any other `[` is still an array. `visit(ListComprehension)` is a
default method that visits the element, list and condition, so existing
`ExpressionVisitor` implementations keep compiling.
@guizmaii
Scan an array once to tell a list comprehension apart
75371f7 
`isListComprehensionAhead()` called `getToken(i)` for each token, which
walks from the current token every time: parsing a 10,000-element array
took seconds. It now follows the token chain.
@guizmaii
guizmaii force-pushed the duckdb-list-comprehension branch from bb13af8 to 75371f7 Compare October 13, 2026 21:57
@manticore-projects
manticore-projects merged commit e7a5a43 into JSQLParser:master Oct 13, 2026
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@manticore-projects

manticore-projects commented Oct 13, 2026

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Thank you much!
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@guizmaii
guizmaii deleted the duckdb-list-comprehension branch October 22, 2026 23:12
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@guizmaii @manticore-projects
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