"=?ISO-8859-1?Q?A=EDlsom_F._Heringer?=" <ailsom@gmail.com> writes:
> At pgAdmin III Query, when I send SELECT * FROM USUARIOS, I get all
> columns correctly. But when I try to get only one column, SELECT senha
> FROM USUARIOS, I get the error message:

> ERROR: column "senha" does not exist

Sounds like a case-sensitivity/quoting issue.  I suggest carefully
reading the rules for quoted and unquoted identifiers explained here:

http://www.postgresql.org/docs/8.2/static/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS

The executive summary is in the last line: "you are advised to always
quote a particular name or never quote it".  I think you probably
created the table using a quoted identifier for "senha", except with
some other capitalization than that.

            regards, tom lane