IssueTracker

- Currently EXERNA_QUERY only allows literal string or query parameter as a 2nd parameter.
- When trying to run query like  ‘SELECT * FROM EXTERNAL_QUERY("CONNECTION", "SELECT * FROM INFORMATION_SCHEMA.TABLES;" || "")’, BQ UI returns ”Unexpected TVF argument type found, expecting literal string at [1:72]” message and doesn’t allow query to run.

It will be nice if it provides more flexibility when composing a query to be thrown to CloudSQL, so that users can dynamically pass arbitrary values as a part of WHERE clause, etc.

(Expected feature example with BQ UI)
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SELECT * FROM EXTERNAL_QUERY("CONNECTION", "SELECT * FROM INFORMATION_SCHEMA.TABLES;" || ""),
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(Expected feature example with BQ CLI)
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bq query --use_legacy_sql=false --parameter='catalog::"def"' --parameter='extquery::SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_CATALOG=@catalog' 'SELECT * FROM EXTERNAL_QUERY("CONNECTION", @extquery)'
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