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Posted to github@datafusion.apache.org by "lovasoa (via GitHub)" <gi...@apache.org> on 2026/01/05 15:26:03 UTC
[PR] Add support for DuckDB `LAMBDA` keyword syntax [datafusion-sqlparser-rs]
lovasoa opened a new pull request, #2149:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2149
## Summary
This PR adds support for parsing DuckDB's `LAMBDA` keyword syntax for lambda functions.
DuckDB supports two syntaxes for lambda functions:
- Arrow syntax: `x -> x + 1` (already supported)
- Lambda keyword syntax: `lambda x : x + 1` (added in this PR)
### Changes
- Added `LAMBDA` keyword to keywords list
- Added `LambdaSyntax` enum to track which syntax style was used (for correct round-tripping)
- Added `parse_lambda_expr()` to parse `lambda <params> : <expr>` syntax
- Updated `LambdaFunction` struct to include `syntax` field
- Added tests for DuckDB lambda functions
### Examples
```sql
-- Single parameter
SELECT list_filter([1, 2, 3], lambda x : x > 1)
-- Multiple parameters (with index)
SELECT list_filter([1, 3, 1, 5], lambda x, i : x > i)
-- Method call syntax
SELECT [3, 4, 5, 6].list_filter(lambda x : x > 4)
```
## Test plan
- [x] Added `test_duckdb_lambda_function` test covering single param, multi-param, and method call syntax
- [x] All existing lambda tests pass (Databricks, ClickHouse, common)
- [x] All DuckDB tests pass
---
> [!NOTE]
> This code was generated by an LLM (Claude) and reviewed by @lovasoa.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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Re: [PR] Add support for DuckDB `LAMBDA` keyword syntax [datafusion-sqlparser-rs]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on PR #2149:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2149#issuecomment-3743856681
(thanks for the review @iffyio )
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Re: [PR] Add support for DuckDB `LAMBDA` keyword syntax [datafusion-sqlparser-rs]
Posted by "lovasoa (via GitHub)" <gi...@apache.org>.
lovasoa commented on PR #2149:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2149#issuecomment-3744375535
@iffyio @alamb thanks for the review! I addressed your comments.
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Re: [PR] Add support for DuckDB `LAMBDA` keyword syntax [datafusion-sqlparser-rs]
Posted by "lovasoa (via GitHub)" <gi...@apache.org>.
lovasoa commented on PR #2149:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2149#issuecomment-3724055602
Hi @iffyio, @alamb ! Do you think you could have a look at this ? The old duckdb lambda syntax is deprecated, so I suppose this is going to pop out more and more. This comes from a bug report in sqlpage.
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Re: [PR] Add support for DuckDB `LAMBDA` keyword syntax [datafusion-sqlparser-rs]
Posted by "iffyio (via GitHub)" <gi...@apache.org>.
iffyio commented on code in PR #2149:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2149#discussion_r2685990664
##########
src/ast/mod.rs:
##########
@@ -1293,14 +1293,39 @@ pub struct LambdaFunction {
pub params: OneOrManyWithParens<Ident>,
/// The body of the lambda function.
pub body: Box<Expr>,
+ /// The syntax style used to write the lambda function.
+ pub syntax: LambdaSyntax,
}
impl fmt::Display for LambdaFunction {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
- write!(f, "{} -> {}", self.params, self.body)
+ match self.syntax {
+ LambdaSyntax::Arrow => write!(f, "{} -> {}", self.params, self.body),
+ LambdaSyntax::LambdaKeyword => {
+ // For lambda keyword syntax, display params without parentheses
+ // e.g., `lambda x, y : expr` not `lambda (x, y) : expr`
+ write!(f, "lambda ")?;
+ match &self.params {
+ OneOrManyWithParens::One(p) => write!(f, "{p}")?,
+ OneOrManyWithParens::Many(ps) => write!(f, "{}", display_comma_separated(ps))?,
+ };
+ write!(f, " : {}", self.body)
+ }
+ }
}
}
+/// The syntax style for a lambda function.
+#[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Copy)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
+pub enum LambdaSyntax {
+ /// Arrow syntax: `param -> expr` or `(param1, param2) -> expr`
+ Arrow,
Review Comment:
Can we add a link to the databricks documentation describing the syntax? https://docs.databricks.com/aws/en/sql/language-manual/sql-ref-lambda-functions
similarly we can add one to the duckdb docs for the lambdakeyword variant
##########
tests/sqlparser_duckdb.rs:
##########
@@ -870,3 +870,22 @@ fn parse_extract_single_quotes() {
let sql = "SELECT EXTRACT('month' FROM my_timestamp) FROM my_table";
duckdb().verified_stmt(sql);
}
+
+#[test]
+fn test_duckdb_lambda_function() {
+ // Test basic lambda with list_filter
+ let sql = "SELECT [3, 4, 5, 6].list_filter(lambda x : x > 4)";
+ duckdb().verified_stmt(sql);
Review Comment:
```suggestion
duckdb_and_generic().verified_stmt(sql);
```
we can cover the generic dialect in the test cases as well?
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Re: [PR] Add support for DuckDB `LAMBDA` keyword syntax [datafusion-sqlparser-rs]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb merged PR #2149:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2149
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