I created a sub query and executed..but it's not throwing up an error.

table1: col1,col2,col3

table2 : r1,r2,r3

 table 1 and table 2 column names are completely different.

I created  a query like

Select col1 from table1 where col1 not in (select col1 from table2) group by col1.

We know that col1 is not in the table2.but the output in coming just the name col1.it’s now throwing up and error like “col1 is invalid in table2”

I am so confused…any help will be appreciated

For a problem like this, you need to privide the exact text of the query.
Taking a initial stab in the dark, it sounds like you may have written the original subquery like:
select 'col1' from table2

If your table2 table does not have a col1 column, then your subquery is simply wrong. Why are you surprised that you get an error for that?

In general, always provide full table names (including owner) with aliases in the FROM clause of your query, and qualify each and every reference to any column with the appropriate alias.

Try this

 

SELECT

col1

FROM

table1 a

Where

a.col1 Not in(Select b.col1 from table2)

group by a.col1