revitalkr opened a new pull request, #2445:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2445
## Summary
For dialects with `supports_left_associative_joins_without_parens = false`,
nested joins are currently created even when no deferred join constraint exists.
## Problem
The non-left-associative join handling was introduced to support deferred
join constraints such as:
A JOIN B JOIN C ON X ON Y
However, the same logic is also applied to queries such as:
A JOIN B LEFT JOIN C ON X
even though there is no deferred ON or USING constraint to attach.
This produces a nested join structure where a flat join chain is expected.
## Solution
Only apply the nesting logic when a deferred join constraint (ON or USING)
remains to be attached.
Queries without deferred constraints continue to use the normal flat join
structure.
## Test
Adds coverage for:
SELECT 'ORIGINAL' AS src,
o.order_id,
c.customer_id,
p.product_id
FROM orders AS o
JOIN customers AS c
LEFT JOIN products AS p
ON p.order_id = o.order_id
and verifies that both Generic and Snowflake dialects produce a flat join
chain (joins.len() == 2).
## Validation - Snowflake script
The following query executes successfully in Snowflake:
SELECT 'ORIGINAL' AS src,
o.order_id,
c.customer_id,
p.product_id
FROM orders AS o
JOIN customers AS c
LEFT JOIN products AS p
ON p.order_id = o.order_id;
and matches the flat interpretation:
(orders AS o JOIN customers AS c)
LEFT JOIN products AS p
ON p.order_id = o.order_id
while the nested interpretation generated by the current
non-left-associative handling:
orders AS o
JOIN (
customers AS c
LEFT JOIN products AS p
ON p.order_id = o.order_id
)
is rejected by Snowflake.
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