I want to perform the following query but i dont know how :

select count(num) from X

and I want the X to be a table from the following query :

select table from bla bla bla . . .

This cannot be done by :select count(num) from (select table from bla bla bla) !

How can i build it ??? I have stuck !

which database is this? because the method you described should work

what was the actual error message you got?

perhaps you could also show real table and column names so we could see if there is an obvious syntax error

I get a incorrect synbtax :

The query is
select count(distinct timestamp) from (select cf.table from general_cfg cf, can c where cf.x1 = c.y1);

This should have worked ???

no, it shouldn't've

the subquery produces an intermediate table result which is used as the data source for the outer query's FROM clause, yes?

well, that intermediate table result has a single column, called "table"

thus, the outer table cannot count the distinct values of a column called "timestamp" because that column doesn't exist

Are we trying to sneak up on dynamic SQL here?

-PatP

And is there a solution to this problem at last ...?????

yes there is!!!!!!!!!!!!

Add an alias name for the table: