check if column is NULL (php)

hi,

the question i have is : is it possible to check in a resultSet - as a
result of pg_query("SELECT ...") - if a column in this result can be set to
NULL.

important : it should work with any select statement - if i use only one
table in the select, i know that i could use pg_meta_data.

i need this for a existing formular generator, which works fine, but i cant
check if NULL values are allowed in this form if i dont know it.

to make it easier to understand what  i mean an example   :

$rs = pg_query("SELECT name,adress,value FROM person, bill");
for ($i = 0; $i < pg_num_rows($rs); $i++ ) {
  $myForm->pushInput(pg_field_name($i),pg_field_type($i), ...);
  // can this field be set to NULL?
  }

thanx

sepp

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