Answers for "how to check value into db using psycopg2 psql"

psycopg2 select example

import psycopg2

try:
   connection = psycopg2.connect(user="sysadmin",
                                  password="pynative@#29",
                                  host="127.0.0.1",
                                  port="5432",
                                  database="postgres_db")
   cursor = connection.cursor()
   postgreSQL_select_Query = "select * from mobile"

   cursor.execute(postgreSQL_select_Query)
   print("Selecting rows from mobile table using cursor.fetchall")
   mobile_records = cursor.fetchall() 
   
   print("Print each row and it's columns values")
   for row in mobile_records:
       print("Id = ", row[0], )
       print("Model = ", row[1])
       print("Price  = ", row[2], "n")

except (Exception, psycopg2.Error) as error :
    print ("Error while fetching data from PostgreSQL", error)

finally:
    #closing database connection.
    if(connection):
        cursor.close()
        connection.close()
        print("PostgreSQL connection is closed")

postgresql psycopg2 select single value

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

import psycopg2
import sys

con = None

try:

    con = psycopg2.connect(database='testdb', user='postgres',
        password='s$cret')

    cur = con.cursor()
    cur.execute('SELECT version()')

    version = cur.fetchone()[0]
    print(version)

except psycopg2.DatabaseError as e:

    print(f'Error {e}')
    sys.exit(1)

finally:

    if con:
        con.close()