The pg_attrdef table stores column default values. The main information about columns is stored in pg_attribute. Only columns that explicitly specify a default value (when the table is created or the column is added) will have an entry here.

Table 1. pg_catalog.pg_attrdef

column type references description
adrelid oid pg_class.oid The table this column belongs to
adnum smallint pg_attribute.attnum The number of the column
adbin text   The internal representation of the column default value
adsrc text   A human-readable representation of the default value. This field is historical, and is best not used.