what is this error mean

the parser is is having difficulty transforming one type into a numeric value.
try an explicit cast.
cast( xxx as numeric )
if that fails then you need to look at what characters are in that string.  Is it Nan +Infinity ???

i dont know what you mean
can you explain it in detail thank you

what do you mean by cast(xxx as numeric)

and waht is NAN + infinity

You have started another thread.  But from the extra information that you have provided there you are trying to equate a numeric column to an empty string, which gives rise to this "invalid input syntax".
(which may be coming from the DBD::PgPP interface)

+- Infinity and Nan are valid IEEE 754 entities.

create table x ( id int, y numeric );

insert into x ( id ) values (1);
insert into x values ( 2, default );
insert into x values ( 3, null );

i insert data into database is base on the data in a text file. that mean i m manually add data into database.

example:
in my text file i have

name  mark
alex   54
helen
david 44

how to make it able to read null in mark as numeric data..