Any limitation in size for return result from SELECT?

Hi,

one question

Select statement returns as a result concatenated all varchar, text and char columns of a table as one single column ...

select col1||col2||col3||.....||col100 from table

However, when the number of concatenated columns is bigger than 22 no result is given back (tested in psql, as well as from pgplsql)....

Most of these columns for the test data are NULL...Datatypes of columns are mixed text, varchar, char...Select statement does not return any error...Just returns a row with a null result....
Any quick suggestions would be very useful....

best regards,
Bulatovic Natasa