How to replace values in joined columns from different tables?

Example:

Source table 1:

1,a1

2,a2

3,a3

Source table 2:

1,b1

2,b2

4,b4

Source table 3:

1,c1

2,c2

3,c3

FIRST QUESTION:

When I join these two tables and I create a table component with the first column to be the first column of the first table and the second column to be the second column of the second table, it displays:

1,b1

2,b2

3,[blank]

I want to replace these blanks with "YES".

SECOND QUESTION:

When I create the table:

1,b1,c1

2,b2,c2

3[blank],c3

I want to replace the values in the third column with 'NO' when there is a blank in either first or second column. When this condition is not met, I would like to leave the values of the third column intact.

Thanks