Databases offer numerous functionalities by which one can manage large amounts of information easily over the web, and high-volume data input and output over a typical file such as a text file. SQL is a query language and is very popular in databases. Many websites use MySQL. SQLite is a “light” version that works over syntax very much similar to SQL.
SQLite is a self-contained, high-reliability, embedded, full-featured, public-domain, SQL database engine. It is the most used database engine in the world wide web.
Python has a library to access SQLite databases, called sqlite3, intended for working with this database which has been included with Python package since version 2.5.
In this article we will discuss, how to query database using commands like Update and Delete and also to visualize data via graphs.
It is recommended to go through SQL using Python | Set 1
Updation and Deletion Operation
# code for update operation import sqlite3 # database name to be passed as parameter conn = sqlite3.connect('mydatabase.db') # update the student record conn.execute("UPDATE Student SET name = 'Sam' where unix='B113059'") conn.commit() print "Total number of rows updated :", conn.total_changes cursor = conn.execute("SELECT * FROM Student") for row in cursor: print row, conn.close() |
Output:
Total number of rows updated : 1 (u'B113053', u'Geek', u'2017-01-11 13:53:39', 21.0), (u'B113058', u'Saan', u'2017-01-11 13:53:39', 21.0), (u'B113059', u'Sam', u'2017-01-11 13:53:39', 22.0)
# code for delete operation import sqlite3 # database name to be passed as parameter conn = sqlite3.connect('mydatabase.db') # delete student record from database conn.execute("DELETE from Student where unix='B113058'") conn.commit() print "Total number of rows deleted :", conn.total_changes cursor = conn.execute("SELECT * FROM Student") for row in cursor: print row, conn.close() |
Output:
Total number of rows deleted : 1 (u'B113053', u'Geek', u'2017-01-11 13:53:39', 21.0), (u'B113059', u'Sam', u'2017-01-11 13:53:39', 22.0)
Data input by User
# code for executing query using input data import sqlite3 # creates a database in RAM con = sqlite3.connect(":memory:") cur = con.cursor() cur.execute("create table person (name, age, id)") print ("Enter 5 students names:") who = [raw_input() for i in range(5)] print ("Enter their ages respectively:") age = [int(raw_input()) for i in range(5)] print ("Enter their ids respectively:") p_id = [int(raw_input()) for i in range(5)] n = len(who) for i in range(n): # This is the q-mark style: cur.execute("insert into person values (?, ?, ?)", (who[i], age[i], p_id[i])) # And this is the named style: cur.execute("select * from person") # Fetches all entries from table print cur.fetchall() |
Output:
(u'Navin', 34, 113053) (u'Basu', 42, 113058) (u'Firoz', 65, 113059) (u'Tim', 47, 113060) (u'Varun', 54, 113061)
Graphing with SQLite
# graph visualization using matplotlib library import matplotlib.pyplot as plt def graph_data(p_id,age): # plotting the points plt.plot(p_id, age, color='yellow', linestyle='dashed', linewidth = 3, marker='*', markerfacecolor='blue', markersize=12) # naming the x axis plt.xlabel('Persons Id') # naming the y axis plt.ylabel('Ages') # plt.plot(p_id,age) plt.show() print ("Enter 5 students names:") who = [raw_input() for i in range(5)] print ("Enter their ages respectively:") age = [int(raw_input()) for i in range(5)] print ("Enter their ids respectively:") p_id = [int(raw_input()) for i in range(5)] # calling graph function graph_data(p_id,age) |
In this way we can perform such operations using SQL query to communicate with Database and plot a Graph significantly to draw out its characteristic.
SQL using Python | Set 1
SQL using Python | Set 3 (Handling large data)
