How to join tables with different columns and different number of rows?

Hello!

What SQL query will help me to concatenate two different tables
with different number of rows? For example , i have first table
with column1 and column2 , having 3 rows , and second table
with column3, column4 , having 5 rows. How to make
third table with column1,column2,column3,column4 and 5 rows in it
(and last two rows in column1 and column2 are empty)

Thanks for sugestions

Igor.