Updating a column in Table A from a Column in Table B during an after insert Trigger Am using MYSQL Workbench

I have a residence table with a sales tax rate and when a new residence record is inserted I want its sales_tax field updated from a tax rate_table. the 2 tables are connected by zip_code.

I am using WORKBENCH Table Triggers to create the code

I have tried several things but I get errors either on syntax or during a load

If I use "UPDATE" I get an error code 1442 which seems to indicate that "UPDATE" is not allowed.

Things I have tried, code generated by workbench

USE infrastructure$$

CREATE DEFINER = CURRENT_USER TRIGGER `infrastructure`.`Residence_AFTER_INSERT` AFTER 
INSERT ON `Residence` FOR EACH ROW
BEGIN

select tr.tax_combined_rate as tax from sales_tax_rate as tr
where residence.res_zip = tr.zip_code;
set residence.res_sales_tax = tax;

END


Result ERROR: Error 1193: Unknown system variable 'res_sales_tax'

I then comment out the line “set residence.res_sales_tax = tax 

Result ERROR: Error 1415: Not allowed to return a result set from a trigger

This error suggests that I can not get a value from another table from within a trigger

Can some one give me some guidance 
Can this be done?
You need a before insert trigger ("after insert", the bird has flown, it's useless modifying the new vales - if MySQL allows you).  In the trigger body, use the following code:

Declare v_tax int;
select tr.tax_combined_rate into v_tax from sales_tax_rate as tr
  where NEW.res_zip = tr.zip_code;
set NEW.res_sales_tax = v_tax;


See the effect here: https://www.db-fiddle.com/f/eEiK6pKGEQEoYL9BPdfooP/0