No Join is required

i Think there is formula 2n-1

where n is the number of table 
so, answer will be 2*10-1=19

There are 2 possible answers
1. No joins required 

Ex: 
SELECT Col1 As Col from Tab1
Union
SELECT Col2 As Col from Tab2
Union
SELECT Col1 As Col from Tab3
... 

2. 9 Joins Required
Ex:
SELECT 
   t1.Col1,
   t2.Col2,
   ....
FROM Tab1 t1
inner join Tab2 t2 on t1.Col1=t2.Col2
inner join Tab3 t3 on t1.Col1=t3.Col2
....

The 10 tables can be joined as,

select table1.columnname,table2.columnname,.....
from table1,table2,.......

It displays 10 fields from 10 different tables.

If there is no relation between tables then no joins.And if 
there relation and you want to fetch related data then 9 
join required if parent table has all foreign key of their  
tables.

Select column1, column2, ...., column10 from table1, 
table2, ..., table10

there are 3 answeres
1. No joins are required if do not want to display related 
data
2.  9 joins are requred if all tables are related
3. no joins reuquired  we can use union if condition is 
like following
select cola from a
union 
select colb from b
union
select colc from c
.
.
.
like wise ten statements

n-1 JOINS
that is 10-1 Join

Or using UNION or UNION all but its not a join

However we will get value from Tables