Method extract_root_and_access_chain

datafusion/sql/src/expr/mod.rs:1087–1126

Extracts the root expression and access chain from a compound expression. This function attempts to identify if a compound expression (like `a.b.c`) should be treated as a column reference with a qualifier (like `table.column`) or as a field access expression. # Arguments `root` - The root SQL expression (e.g., the first part of `a.b.c`) `access_chain` - Vector of access expressions (e.g., `.b`

(
        &self,
        root: SQLExpr,
        mut access_chain: Vec<AccessExpr>,
        schema: &DFSchema,
        planner_context: &mut PlannerContext,
    )

    /// * The resolved root expression
    /// * The remaining access chain that should be processed as field accesses
    fn extract_root_and_access_chain(
        &self,
        root: SQLExpr,
        mut access_chain: Vec<AccessExpr>,
        schema: &DFSchema,
        planner_context: &mut PlannerContext,
    ) -> Result<(Expr, Vec<AccessExpr>)> {
        let SQLExpr::Identifier(root_ident) = root else {
            let root = self.sql_expr_to_logical_expr(root, schema, planner_context)?;
            return Ok((root, access_chain));
        };

        let mut compound_idents = vec![root_ident];
        let first_non_ident = access_chain
            .iter()
            .position(|access| !matches!(access, AccessExpr::Dot(SQLExpr::Identifier(_))))
            .unwrap_or(access_chain.len());
        for access in access_chain.drain(0..first_non_ident) {
            if let AccessExpr::Dot(SQLExpr::Identifier(ident)) = access {
                compound_idents.push(ident);
            } else {
                return internal_err!("Expected identifier in access chain");
            }
        }

        let root = if compound_idents.len() == 1 {
            self.sql_identifier_to_expr(
                compound_idents.pop().unwrap(),
                schema,
                planner_context,
            )?
        } else {
            self.sql_compound_identifier_to_expr(
                compound_idents,
                schema,
                planner_context,
            )?
        };
        Ok((root, access_chain))
    }

    fn sql_compound_field_access_to_expr(
        &self,