Function plan_query 

pub fn plan_query(
    query: &Query,
    catalog: &dyn SqlCatalog,
    functions: &FunctionRegistry,
    temporal: TemporalScope,
) -> Result<SqlPlan>

Plan a nested SELECT query: a subquery, CTE body, UNION branch, derived table, INSERT source, or MERGE source. Its SELECT list refuses a sequence accessor over a relation.