[FEATURE] Support for outer join semantics

Feature Description

Outer join semantics are useful in SQL, but do not make sense for parameterisation of HTTP methods. This feature request is for:

• support of inequality join predicates where they make sense.
• decent error messaging where they are supplied but disallowed.
• probably classic case for v1 outer joins is some sort of insert into... t1 LEFT OUTER JOIN t2 on t1.some_col = t2.some_col where t2.some_col is null; motivated by desired or expected absence.

Example(s)
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Possible Approaches or Libraries to Consider
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Additional context
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No files, tests, or entry points are named. First clarify which SQL join forms and inequality predicates are in scope, how they relate to HTTP method parameterization, and what error behavior and v1 support should be considered done.