why sometimes while writing code it gives an error and then when I open another browser it works fine there .
and it does not even show whats the error message …
Thanks for getting in touch! Can you provide any more specific details about the issues you’re encountering? There are a lot of different reasons you may be encountering errors in some cases and not in others. Many are related to the connection lifecycle—if your client/programming language library/etc. isn’t configured with logic for handling disconnections (e.g. using a connection pool), you may encounter intermittent errors.
for example 
SELECT O.EMPLOYEEID, ORDERID, SHIPCITY, CUSTOMERID
from “alanparadise/nw”.“orders” O
WHERE EMPLOYEEID IN
(SELECT EMPLOYEEID FROM “ALANPARADISE/NW”.“EMPLOYEES” E
WHERE E.CITY = O.SHIPCITY);
this worked perfectly fine once and second time its showing error message .
I see a couple of issues here:
- curly quotes (“”) will cause issues in Postgres. Make sure you’re using straight quotes (
""). In many cases, if you’re using word processing software such as MS Word or google docs, straight quotes will get replaced by curly quotes. Make sure you’re using an editor or IDE intended for code rather than prose. (this may just be an issue of copying into discourse. If you include your examples in backticks (``) they will render exactly as you write them, e.g.select * from ...) - identifiers within quotes are case sensitive. “ALANPARADISE/NW”.“EMPLOYEES” is probably not correct.
You may also find this article in our docs helpful as it pertains to the alanparadise database/course: FAQs for "The Structured Query Language" on Coursera
Thanks Daniel. I will try to amend the mistakes and see if it works.Appreciate your help.