[vishalmore90]

Fixes #41052.

Description

In Beam YAML, _SqlJoinTransform generated invalid SQL queries when joining three or more inputs in topologies or dictionary key orderings that did not match a star topology centered at tables[0]. This caused two failure modes:

1. Tables joining downstream tables were left without an ON clause (INNER JOIN tableB INNER JOIN tableC ON ...), leading to Calcite SqlParseException.
2. Tables were referenced in preceding ON clauses before being joined into the query scope.
3. In _parse_fields, specifying '*' as explicitly documented in _SqlJoinTransform raised a ValueError.

This PR:

• Replaces the linear table iteration with an adjacency graph traversal (BFS) starting at tables[0]. Each newly joined table is connected to already visited tables with all connecting predicates placed into its ON clause, guaranteeing valid SQL scoping and syntax.
• Supports cols == '*' in _parse_fields.
• Adds unit tests in yaml_join_test.py covering multi-table arbitrary order joins, cycle/triangle joins, and wildcard field parsing.
• Updates CHANGES.md.

[github-actions]

📋 Review Summary

This PR resolves #41052 by constructing an adjacency graph from the parsed join equalities and traversing connected tables from tables[0] rather than iterating blindly in input dictionary order. This guarantees every JOIN clause has a valid ON condition and only references tables already introduced in the FROM/JOIN sequence. It also fixes multi-table outer join propagation across visited tables and adds '*' wildcard support in _parse_fields.

🔍 General Feedback

• The graph traversal and composite ON clause construction cleanly handle arbitrary input orderings, multi-hop chains, and cyclic/triangle join predicates.
• Adding SqlJoinQueryTest to validate the generated SQL strings directly without requiring an external runner/expansion service provides good precommit test coverage.

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[github-actions]

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R: @derrickaw for label yaml.
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