2010YOUY01 commented on code in PR #23738:
URL: https://github.com/apache/datafusion/pull/23738#discussion_r3643581168
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datafusion/sql/src/unparser/plan.rs:
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@@ -115,6 +115,7 @@ impl Unparser<'_> {
| LogicalPlan::Aggregate(_)
| LogicalPlan::Sort(_)
| LogicalPlan::Join(_)
+ | LogicalPlan::AsOfJoin(_)
Review Comment:
I think @Xuanwo proposed to implement Snowflake syntax (with
`match_condition` keyword)
https://docs.snowflake.com/en/sql-reference/constructs/asof-join
Personally I also think Snowflake syntax is better than the DuckDB syntax
```
-- DuckDB synatx
SELECT t.*, p.price
FROM trades t
ASOF JOIN prices p
ON t.symbol = p.symbol AND t.when >= p.when;
-- Snowflake syntax
SELECT t.*, p.price
FROM trades t
ASOF JOIN prices p
MATCH_CONDITION t.when >= p.when
ON t.symbol = p.symbol;
```
The reason is the in-equality predicate has different semantical meaning:
- equal condition: pre-filter all pairs before the ASOF join step
- in-equality condition: for all satisfied `prices` table rows, only return
the closest match
Separating them is more intuitive given the special semantics of ASOF joins.
The downside is that we informally use DuckDB as our primary reference
system, so following Snowflake here might depart from that convention.
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