Problems with joining two tables - Mailing list pgsql-sql

Hi,

I have two tables, the first one has one column as a reference to the index of the second. Not every row in the first
tablehas a reference to the second table. I now want to make a query to get all information of the first table and, if
thereis a reference, the corresponding information of the second table in that row. In another programming language I
wouldjust make an if-clause but how can I do this in SQL?
 

Thanks for your help

Michael