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.

    columntypereferencesdescription
    adrelidoidpg_class.oidThe table this column belongs to
    adnumint2pg_attribute.attnumThe number of the column
    adbintext The internal representation of the column default value
    adsrctext A human-readable representation of the default value. This field is historical, and is best not used.

    Parent topic: System Catalogs Definitions