Change query generator to use INNER JOIN

[feordin]

Description

Update the SQL Query generator to use INNER JOIN instead of EXISTS when joining CTEs. This dramatically reduces the overhead for SQL to create the query plan.

Related issues

Addresses [issue AB#105397].

Testing

Manual testing file of the customer's reported failing query was created and used as a guide. The failure to generate the query plan was observed locally.

FHIR Team Checklist

• Update the title of the PR to be succinct and less than 65 characters
• Add a milestone to the PR for the sprint that it is merged (i.e. add S47)
• Tag the PR with the type of update: Bug, Build, Dependencies, Enhancement, New-Feature or Documentation
• Tag the PR with Open source, Azure API for FHIR (CosmosDB or common code) or Azure Healthcare APIs (SQL or common code) to specify where this change is intended to be released.
• Tag the PR with Schema Version backward compatible or Schema Version backward incompatible or Schema Version unchanged if this adds or updates Sql script which is/is not backward compatible with the code.
• CI is green before merge
• Review squash-merge requirements

Semver Change (docs)

Patch|Skip|Feature|Breaking (reason)

[mikaelweave]

Small comment on code and questions on the REST file.

[mikaelweave]

Not an expert in this area but looks good to me. Approved assuming expert isn't needed.