#!/usr/bin/env python
# -*- coding: utf-8 -*-

#--------- define Interface
##PostgreSQL/PostGIS Tools=group
##Drop default value/sequence=name
##PostgreSQL_Table=vector
##Column=field PostgreSQL_Table

from PyQt4.QtCore import *
from PyQt4.QtGui import *
from PyQt4 import *

from qgis.core import *
from qgis.gui import *
from qgis.utils import *

import psycopg2

#get the parameters for the tpg table into a directory
#get the table
pg_table = processing.getObject(PostgreSQL_Table)
#create empty dictionary for key/value pairs of the tables connection parameters
db_params = {}
db_params['clmn'] = Column
#iterate over connection string
progress.setInfo(20*'-' + '  Connection parameters')
for param in pg_table.dataProvider().dataSourceUri().split(' '):
    key_val = param.split('=')
    progress.setInfo(str(key_val))
    try:
        #set key/value pair
        db_params[key_val[0]] = key_val[1]
    except:
        pass

#generate the sql statement string
#the text in round brackets are the keys from the db_params dictionary created above
#the values belonging to the keys are inserted into the string
progress.setInfo(20*'-' + '  SQL statement')
sql = """ALTER TABLE %(table)s
ALTER COLUMN %(clmn)s DROP DEFAULT;
DROP SEQUENCE IF EXISTS %(table)s_%(clmn)s_seq;
COMMIT;""" % db_params
#remove double quotes
sql = sql.replace('"','')
progress.setInfo(sql)

#make connection string
constr = """dbname=%(dbname)s host=%(host)s port=%(port)s user=%(user)s password=%(password)s""" % db_params
progress.setInfo(20*'-' + '  DB Connection string')
progress.setInfo(constr)
#make db connection
con = psycopg2.connect(constr)
cur = con.cursor()
#execute the above created sql statement
progress.setInfo(20*'-' + '  Executing SQL statement ...')
cur.execute(sql)
progress.setInfo(20*'-' + '  ... done.')

SELECT column_default
FROM information_schema.columns
WHERE (table_schema, table_name, column_name) = ('/*schema*/', '/*table*/', '/*column*/');