feat: support ASOF JOIN SQL - #23830
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# Conflicts: # datafusion/expr/src/logical_plan/builder.rs # datafusion/expr/src/logical_plan/plan.rs
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cc @2010YOUY01, this PR is good to go! 🚀 Also CC @jayzhan211: would you like to follow this stack's review? Happy to ping you if you're interested. 😄 |
Of course! |
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Thanks @Xuanwo Minor issues left, others LGTM
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Thank you, this is great as always. Here is some sugestions:
Before merging
- I left a few suggestions on the logical plan APIs — curious what you think. If we can agree on that, let's update them before merging.
- Add some simple tests for the unparser.
Potential follow-ups
- Consolidate the Rust integration tests into
slt. - More
sltcoverage. Below is the coverage gap suggested by AI:
Click to expand
ASOF slt: extra coverage
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Outer WHERE on a right column must stay above the join
Only correctness property with no guard. If filter pushdown later learns
about ASOF and pushes this into the right input, candidate selection changes.
SELECT l.id, r.val FROM asof_left l ASOF JOIN asof_right r
MATCH_CONDITION (l.ts >= r.ts) ON l.grp = r.grp WHERE r.val <> 'a6';
Expect: EXPLAIN shows Filter above AsOf Join; ids 2,4,5 (id 3 dropped, not remapped to a4). -
Projection pruning through the node
Existing EXPLAINs select every column, so they can't show pruning.
EXPLAIN SELECT l.id FROM asof_left l ASOF JOIN asof_right r
MATCH_CONDITION (l.ts >= r.ts) ON l.grp = r.grp;
Expect: TableScan: asof_right projection=[grp, ts] -
SELECT * with USING
Docs promise the key appears once; file only selects named columns.
SELECT * FROM asof_left l ASOF JOIN asof_right r
MATCH_CONDITION (l.ts >= r.ts) USING (grp);
Expect: 5 columns (id, grp, ts, ts, val), not 6. -
Expression operands
Every test uses bare columns; side-ownership check on expressions is untested.
MATCH_CONDITION (l.ts >= r.ts + INTERVAL '1 second')
ON lower(l.grp) = lower(r.grp) -
Reversed equality sides in ON
The main thing asof_join_on adds; only unit-tested in the builder.
ON r.grp = l.grp -- same result as l.grp = r.grp -
Ordered types beyond timestamp/int
String, DATE vs TIMESTAMP, float, tz/precision mismatch, dictionary keys.
ON l.grp = r.grp where l.grp is arrow_cast(grp, 'Dictionary(Int32, Utf8)')
Dictionary matters most: Parquet produces it. -
Empty inputs
ASOF JOIN (SELECT * FROM asof_right WHERE false) r ... -- all r.* NULL
FROM (SELECT * FROM asof_left WHERE false) l ... -- zero rows -
Duplicate left rows emitted once each
FROM (SELECT * FROM asof_left UNION ALL SELECT * FROM asof_left) l ...
Expect: 14 rows, each id twice with same match. -
Self join
FROM asof_left a ASOF JOIN asof_left b MATCH_CONDITION (a.ts > b.ts) ON a.grp = b.grp -
Composition through the planner
ASOF then inner join, GROUP BY over output, CREATE VIEW, WITH ... AS.
... ASOF JOIN asof_right r MATCH_CONDITION (...) ON ... JOIN asof_right r2 ON r.val = r2.val -
USING with multiple keys
USING (venue, grp) -
Unpinned error messages
Rust test only asserts "is_err"; none of these messages are checked anywhere.
MATCH_CONDITION (1 >= r.ts) -> left operand must reference only the left input
ON 1 = 1 -> must compare one left expression with one right
MATCH_CONDITION (l.ts >= r.ts AND ...) -> requires <, <=, >, or >=, found AND
ON l.grp = l.grp -> must compare one left expression with one right
ON l.grp = r.grp AND l.ts >= r.ts -> accepts only equality conditions combined with AND
SELECT ts ... USING (grp) -> Ambiguous reference to unqualified field ts
unbounded left table -> AsOfJoinExec requires bounded inputs
Note: NATURAL ASOF JOIN is rejected by sqlparser, so the planner branch is unreachable. -
EXPLAIN for the other two forms
USING shows constraint=Using; no-key form shows on=[] in the physical plan. -
Comment on deferred optimizations
Filter/limit pushdown into the left input and order reuse by ORDER BY
don't happen yet. A note saves the next person from thinking it's a bug.
| Ok(()) | ||
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| fn register_asof_test_tables(ctx: &SessionContext) -> Result<()> { |
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Can we unify those tests into sqllogictests, this way I think it's easier to maintain. Unless there are some setups that is not possible to do in slt, we might want extra coverage here.
In order to move those tests checking partition properties, I think we can assert the end behavior (final plan shape), rather than internal properties.
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Agreed for the SQL-level cases. I kept the Rust tests that need multi-partition plans, unbounded inputs, or plan-to-SQL roundtrips. I’ll consolidate the remaining overlap in a follow-up.
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| // Keep ASOF-specific locals out of the recursive plan unparser's stack frame. | ||
| #[inline(never)] | ||
| fn asof_join_to_sql( |
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I don't fully understand the unparser now, but my AI tool suggest it is good to go, with some cleanup advices:
AI review
The unparser is heavy relative to the join it mirrors. About 120 lines of branching on "already projected" versus not, and "needs a derived subquery" versus not, for each side. The regular join unparser has the same structural problem, so this is inherited rather than introduced. A cleaner alternative would be a small shared helper that takes a join input and returns both the relation and its projection items, used by both join kinds. That refactor is bigger than this PR should carry, but it would be a natural follow-up given the branch already touched the shared nesting helper.
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Will treat this change as a follow up
| MATCH_CONDITION (l.ts = r.ts) | ||
| ON l.grp = r.grp; | ||
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| query error ASOF MATCH_CONDITION left operand must reference only the left input |
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Should this query get normalized internally, and make it valid? 🤔
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I’d keep this invalid. Snowflake defines MATCH_CONDITION operand order semantically, so the left input must remain on the left. ON equality operands are still accepted in either order.
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I see, that's the snowflake behavior.
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Thank you @jayzhan211 @2010YOUY01 for the review! I have updated the builder API and added direct unparser coverage, including nested ASOF inputs. I kept the setup-dependent Rust tests here and will handle broader SLT consolidation separately. |
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Thank you for opening this pull request! Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch). Details |
Sounds like a good plan! |
4 participants
Which issue does this PR close?
Rationale for this change
This is the SQL frontend layer of the ASOF JOIN stack. It adds syntax and
unparsing on top of the merged physical and logical contracts. The PR now
contains only the isolated SQL frontend diff.
What changes are included in this PR?
ASOF JOIN ... MATCH_CONDITION (...)with optionalONorUSINGequality keys.
ONpredicates.nested join scope.
USINGkeys, left-partitioned broadcast execution, the full-right memoryrequirement, repeated scans, and the absence of spill/repartitioned ASOF.
coercion, equality-free joins, USING, invalid contracts, EXPLAIN, boundedness,
and optimized-plan round trips.
partitioning is preserved while the right input is single-partitioned.
Are these changes tested?
Yes:
cargo fmt --all./ci/scripts/doc_prettier_check.sh --write --allow-dirtycargo clippy --all-targets --all-features -- -D warningscargo test -p datafusion --test core_integration asof --all-featurescargo test -p datafusion-sqllogictest --test sqllogictests --all-features -- asof_joinAre there any user-facing changes?
Users can express Snowflake-style ASOF joins in SQL with
MATCH_CONDITION, optional equality keys, and<,<=,>, or>=matchdirections. With
USING, wildcard output exposes one unqualified key whileboth qualified input keys remain addressable. The user guide also documents
the initial broadcast strategy and its memory/no-spill limitations.
#23829 and #23828 are merged. This is the next core layer in the ASOF stack and
does not depend on the optional floating-point follow-up #24375.