Function sql_impl_table_func_inner

src/sql/src/func.rs:438–486

Defines a built-in table function from a static SQL SELECT statement. The SQL statement should use the standard parameter syntax (`$1`, `$2`, ...) to refer to the inputs to the function; see sql_impl_func for an example. The number of parameters in the SQL expression must exactly match the number of parameters in the built-in's declaration. There is no support for variadic functions. As this is

(
    sql: &'static str,
    feature_flag: Option<&'static vars::FeatureFlag>,
)

// table function. The SELECT's projection's names are used and should be
// aliased if needed.
fn sql_impl_table_func_inner(
    sql: &'static str,
    feature_flag: Option<&'static vars::FeatureFlag>,
) -> Operation<TableFuncPlan> {
    let query = match mz_sql_parser::parser::parse_statements(sql)
        .expect("static function definition failed to parse")
        .expect_element(|| "static function definition must have exactly one statement")
        .ast
    {
        Statement::Select(SelectStatement { query, as_of: None }) => query,
        _ => panic!("static function definition expected SELECT statement"),
    };
    let invoke = move |qcx: &QueryContext, types: Vec<SqlScalarType>| {
        // Reconstruct an expression context where the parameter types are
        // bound to the types of the expressions in `args`.
        let mut scx = qcx.scx.clone();
        scx.param_types = RefCell::new(
            types
                .into_iter()
                .enumerate()
                .map(|(i, ty)| (i + 1, ty))
                .collect(),
        );
        let mut qcx = QueryContext::root(&scx, qcx.lifetime);

        let query = query.clone();
        let (mut query, new_ids) = names::resolve(qcx.scx.catalog, query)?;
        scx.sql_impl_resolved_ids
            .lock()
            .expect("planning is single-threaded")
            .extend_from(&new_ids);
        transform_ast::transform(&scx, &mut query)?;

        query::plan_nested_query(&mut qcx, &query)
    };

    Operation::variadic(move |ecx, args| {
        if let Some(feature_flag) = feature_flag {
            ecx.require_feature_flag(feature_flag)?;
        }
        let types = args.iter().map(|arg| ecx.scalar_type(arg)).collect();
        let (mut expr, scope) = invoke(ecx.qcx, types)?;
        expr.splice_parameters(&args, 0);
        Ok(TableFuncPlan {
            imp: TableFuncImpl::Expr(expr),
            column_names: scope.column_names().cloned().collect(),
        })
    })
}

/// Implements a table function using SQL.
///