Add support for PostgreSQL's ORDER BY ... USING <operator> clause by LucaCappelletti94 · Pull Request #2246 · apache/datafusion-sqlparser-rs

LucaCappelletti94 · 2026-02-26T19:49:51Z

This PR adds parser and AST support for PostgreSQL USING operators in ORDER BY expressions, including:

top-level ORDER BY
aggregate argument list ORDER BY (e.g. inside aggfns(...) / string_agg(...) style clauses)

Problem

sqlparser-rs previously rejected valid PostgreSQL statements containing:

ORDER BY <expr> USING <operator>

with errors like:

Expected: ), found: using

This blocked parsing of several PostgreSQL regression-style aggregate statements.

Root Cause

parse_order_by_expr_inner only supported:

ASC | DESC
NULLS FIRST | NULLS LAST

and had no branch to parse USING <operator>.

Dialect Scope Decision

ORDER BY ... USING <operator> is intentionally enabled for PostgreSQL only.

Rationale:

PostgreSQL explicitly documents ORDER BY expression [ USING operator ] ... in SELECT.
Other dialects supported by this repository generally document ORDER BY with expression + ASC|DESC (+ null ordering), but not USING <operator>.

References:

Complete Examples

PostgreSQL: accepted

SELECT a FROM t ORDER BY a USING <;

SELECT a FROM t ORDER BY a USING OPERATOR(pg_catalog.<) NULLS LAST;

SELECT aggfns(DISTINCT a, a, c ORDER BY c USING ~<~, a)
FROM (VALUES (1,3,'foo'),(0,NULL,NULL),(2,2,'bar'),(3,1,'baz')) v(a,b,c),
     generate_series(1,2) i;

CREATE OR REPLACE VIEW agg_view1 AS
SELECT aggfns(a,b,c ORDER BY c USING ~<~)
FROM (VALUES (1,3,'foo'),(0,NULL,NULL),(2,2,'bar'),(3,1,'baz')) v(a,b,c);

PostgreSQL: rejected (invalid syntax)

SELECT a FROM t ORDER BY a USING ;
-- Error: Expected an ordering operator after USING

SELECT a FROM t ORDER BY a USING OPERATOR();
-- Error: Expected an operator name

SELECT a FROM t ORDER BY a USING < DESC;
-- Error: ASC/DESC cannot be used together with USING in ORDER BY

iffyio · 2026-03-02T11:58:16Z

src/parser/mod.rs

+        }
+    }
+
+    fn is_valid_order_by_using_operator_symbol(symbol: &str) -> bool {


is this code necessary?

Removed, parse_order_by_using_operator now uses dialect.is_custom_operator_part(...) directly. No separate symbol-check helper anymore. I wasn't aware there was a dialect helper method.

iffyio · 2026-03-02T11:59:01Z

src/parser/mod.rs


-        let options = self.parse_order_by_options()?;
+        let using_operator = if !with_operator_class
+            && dialect_of!(self is PostgreSqlDialect)


if we need to dialect guard this, I think we can introduce a dialect method instead of the macro

Added supports_order_by_using_operator() on Dialect (default false), enabled in PostgreSqlDialect, and parser now checks that method instead of dialect_of!. I double checked that no other dialect supports it at this time.

iffyio · 2026-03-02T12:00:08Z

src/parser/mod.rs

+                Token::Word(w)
+                    if w.quote_style.is_none() && terminal_keywords.contains(&w.keyword) =>
+                {
+                    break;


are these diffs required for this PR?

No, it was nightly clippy fixes. Removed from git history.

iffyio · 2026-03-02T12:01:23Z

tests/sqlparser_postgres.rs

+    );
+
+    // `USING` in ORDER BY is PostgreSQL-specific and should not parse in GenericDialect.
+    let generic = TestedDialects::new(vec![Box::new(GenericDialect {})]);


note, per the dialect comment, we'd want to avoid hardcoding dialects in tests

Replaced the GenericDialect negative case with a local wrapper dialect that behaves like Postgres but returns false for supports_order_by_using_operator().

LucaCappelletti94 · 2026-03-03T13:21:08Z

I’ve applied the requested changes and force-pushed the branch, so to remove irrelevant clippy changes from the commits.

Replaced the hardcoded parser guard (dialect_of!(...PostgreSqlDialect)) with a dialect capability method: Dialect::supports_order_by_using_operator(), enabled in PostgreSqlDialect only. I have also spent a bit of time checking yet again if any other dialects had it, but so far no other dialects support it.
Removed the dedicated is_valid_order_by_using_operator_symbol helper and now validate USING operators through existing dialect behavior (dialect.is_custom_operator_part(...)), so we don’t duplicate operator-character rules in parser code.
Trimmed the PR scope/history to a single focused commit and removed unrelated nightly clippy code smell fixes - I hadn't realized it was a nightly only rant.

iffyio · 2026-03-04T13:40:21Z

src/parser/mod.rs

+        let using_operator = if !with_operator_class
+            && self.dialect.supports_order_by_using_operator()
+            && self.parse_keyword(Keyword::USING)
+        {
+            Some(self.parse_order_by_using_operator()?)
+        } else {
+            None
+        };
+
+        let options = if using_operator.is_some() {
+            if self
+                .peek_one_of_keywords(&[Keyword::ASC, Keyword::DESC])
+                .is_some()
+            {
+                return parser_err!(
+                    "ASC/DESC cannot be used together with USING in ORDER BY".to_string(),
+                    self.peek_token_ref().span.start
+                );
+            }
+            OrderByOptions {
+                asc: None,
+                nulls_first: self.parse_order_by_nulls_first_last(),
+            }


would it be possible to use something like this representation instead?

pub enum OrderByExpr { Asc, Desc, Using(...), UsingOperator(...), } pub struct OrderByOptions { pub expr: Option<OrderByExpr>, pub nulls_first: Option<bool>, }

iffyio · 2026-03-04T13:42:13Z

tests/sqlparser_postgres.rs

+    #[derive(Debug)]
+    struct OrderByUsingDisabledDialect;
+
+    impl Dialect for OrderByUsingDisabledDialect {
+        fn is_identifier_start(&self, ch: char) -> bool {
+            PostgreSqlDialect {}.is_identifier_start(ch)
+        }
+
+        fn is_identifier_part(&self, ch: char) -> bool {
+            PostgreSqlDialect {}.is_identifier_part(ch)
+        }
+
+        fn supports_order_by_using_operator(&self) -> bool {
+            false
+        }
+    }
+
+    let without_order_by_using = TestedDialects::new(vec![Box::new(OrderByUsingDisabledDialect)]);
+    assert!(without_order_by_using
+        .parse_sql_statements("SELECT a FROM t ORDER BY a USING <;")


I think we can have the tests in common.rs instead to cover dialects via the all_dialects_where(|d| d.support*) pattern. Since the impl is guarded by the dialect method vs explicit to postgres

iffyio · 2026-03-04T13:43:04Z

src/ast/query.rs

 pub struct OrderByExpr {
    /// The expression to order by.
    pub expr: Expr,
+    /// Optional PostgreSQL `USING <operator>` clause.


can we include reference doc to maybe this?
https://www.postgresql.org/docs/current/sql-select.html

so folks know where to find this feature easily

LucaCappelletti94 marked this pull request as ready for review February 26, 2026 19:55

iffyio reviewed Mar 2, 2026

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PostgreSQL: support ORDER BY USING via dialect capability

7c2e3b6

LucaCappelletti94 force-pushed the postgres-regression-2 branch from 3b2da72 to 7c2e3b6 Compare March 2, 2026 21:19

LucaCappelletti94 added 2 commits March 2, 2026 22:51

Merge branch 'main' into postgres-regression-2

ca32b8f

Merge branch 'main' into postgres-regression-2

e8056c7

iffyio reviewed Mar 4, 2026

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Add support for PostgreSQL's ORDER BY ... USING <operator> clause#2246

Add support for PostgreSQL's ORDER BY ... USING <operator> clause#2246
LucaCappelletti94 wants to merge 3 commits intoapache:mainfrom
LucaCappelletti94:postgres-regression-2

LucaCappelletti94 commented Feb 26, 2026

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LucaCappelletti94 commented Mar 3, 2026

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LucaCappelletti94 commented Feb 26, 2026

Problem

Root Cause

Dialect Scope Decision

Complete Examples

PostgreSQL: accepted

PostgreSQL: rejected (invalid syntax)

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LucaCappelletti94 commented Mar 3, 2026

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