I have a schema like :

• employees (eno, ename, zip, hdate)
• customers (cno, cnmae, street, zip, phone)
• zipcodes (zip, city)

where zip is pk in zipcodes and fk in other tables.
I have to write an update query which updates all the occurence of zipcode 4994 to 1234 throughout the database.

update zipcodes,customers,employees  
  set zip = 0  
where customers.zip = zipcodes.zip 
  and employees.zip = zipcodes.zip;  

but i know i am not doing it right. Is there a way to update all the tables zip ina single update query?