Method show_columns_to_plan

datafusion/sql/src/statement.rs:2514–2550

(
        &self,
        extended: bool,
        full: bool,
        sql_table_name: ObjectName,
    )

    }

    fn show_columns_to_plan(
        &self,
        extended: bool,
        full: bool,
        sql_table_name: ObjectName,
    ) -> Result<LogicalPlan> {
        // Figure out the where clause
        let where_clause = object_name_to_qualifier(
            &sql_table_name,
            self.options.enable_ident_normalization,
        )?;

        if !self.has_table("information_schema", "columns") {
            return plan_err!(
                "SHOW COLUMNS is not supported unless information_schema is enabled"
            );
        }

        // Do a table lookup to verify the table exists
        let table_ref = self.object_name_to_table_reference(sql_table_name)?;
        let _ = self.context_provider.get_table_source(table_ref)?;

        // Treat both FULL and EXTENDED as the same
        let select_list = if full || extended {
            "*"
        } else {
            "table_catalog, table_schema, table_name, column_name, data_type, is_nullable"
        };

        let query = format!(
            "SELECT {select_list} FROM information_schema.columns WHERE {where_clause}"
        );

        let mut rewrite = DFParser::parse_sql(&query)?;
        assert_eq!(rewrite.len(), 1);
        self.statement_to_plan(rewrite.pop_front().unwrap()) // length of rewrite is 1
    }

    /// Rewrite `SHOW FUNCTIONS` to another SQL query
    /// The query is based on the `information_schema.routines` and `information_schema.parameters` tables