Read Operation

The SELECT statement is used to read the values from the databases. We can restrict the output of a select query by using various clause in SQL like where, limit, etc.

Python provides the fetchall() method returns the data stored inside the table in the form of rows. We can iterate the result to get the individual rows.

In this section of the tutorial, we will extract the data from the database by using the python script. We will also format the output to print it on the console.

Example

snippet
import mysql.connector

#Create the connection object 
myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")

#creating the cursor object
cur = myconn.cursor()

try:
    #Reading the Employee data    
    cur.execute("select * from Employee")

    #fetching the rows from the cursor object
    result = cur.fetchall()
    #printing the result
    
    for x in result:
        print(x);
except:
    myconn.rollback()

myconn.close()

Output:

Output
('John', 101, 25000.0, 201, 'Newyork') ('John', 102, 25000.0, 201, 'Newyork') ('David', 103, 25000.0, 202, 'Port of spain') ('Nick', 104, 90000.0, 201, 'Newyork') ('Mike', 105, 28000.0, 202, 'Guyana')

Reading specific columns

We can read the specific columns by mentioning their names instead of using star (*).

In the following example, we will read the name, id, and salary from the Employee table and print it on the console.

Example

snippet
import mysql.connector
#Create the connection object 
myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
#creating the cursor object
cur = myconn.cursor()
try:
    #Reading the Employee data    
    cur.execute("select name, id, salary from Employee")

    #fetching the rows from the cursor object
    result = cur.fetchall()
    #printing the result
    for x in result:
        print(x);
except:
    myconn.rollback()
myconn.close()

Output:

Output
('John', 101, 25000.0) ('John', 102, 25000.0) ('David', 103, 25000.0) ('Nick', 104, 90000.0) ('Mike', 105, 28000.0)

The fetchone() method

The fetchone() method is used to fetch only one row from the table. The fetchone() method returns the next row of the result-set.

Consider the following example.

Example

snippet
import mysql.connector

#Create the connection object 
myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")

#creating the cursor object
cur = myconn.cursor()

try:
    #Reading the Employee data    
    cur.execute("select name, id, salary from Employee")

    #fetching the first row from the cursor object
    result = cur.fetchone()

    #printing the result
    print(result)

except:
    myconn.rollback()
    
myconn.close()

Output:

Output
('John', 101, 25000.0)

Formatting the result

We can format the result by iterating over the result produced by the fetchall() or fetchone() method of cursor object since the result exists as the tuple object which is not readable.

Consider the following example.

Example

snippet
import mysql.connector

#Create the connection object 
myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")

#creating the cursor object
cur = myconn.cursor()

try:

    #Reading the Employee data    
    cur.execute("select name, id, salary from Employee")

    #fetching the rows from the cursor object
    result = cur.fetchall()

    print("Name    id    Salary");
    for row in result:
        print("%s    %d    %d"%(row[0],row[1],row[2]))
except:
    myconn.rollback()

myconn.close()

Output:

Output
Name id Salary John 101 25000 John 102 25000 David 103 25000 Nick 104 90000 Mike 105 28000

Using where clause

We can restrict the result produced by the select statement by using the where clause. This will extract only those columns which satisfy the where condition.

Consider the following example.

Example: printing the names that start with j

snippet
import mysql.connector

#Create the connection object 
myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")

#creating the cursor object
cur = myconn.cursor()

try:
    #Reading the Employee data    
    cur.execute("select name, id, salary from Employee where name like 'J%'")

    #fetching the rows from the cursor object
    result = cur.fetchall()

    print("Name    id    Salary");

    for row in result:
        print("%s    %d    %d"%(row[0],row[1],row[2]))
except:
    myconn.rollback()

myconn.close()

Output:

Output
Name id Salary John 101 25000 John 102 25000

Example: printing the names with id = 101, 102, and 103

snippet
import mysql.connector

#Create the connection object 
myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")

#creating the cursor object
cur = myconn.cursor()

try:
    #Reading the Employee data    
    cur.execute("select name, id, salary from Employee where id in (101,102,103)")

    #fetching the rows from the cursor object
    result = cur.fetchall()

    print("Name    id    Salary");

    for row in result:
        print("%s    %d    %d"%(row[0],row[1],row[2]))
except:
    myconn.rollback()
    
myconn.close()

Output:

Output
Name id Salary John 101 25000 John 102 25000 David 103 2500

Ordering the result

The ORDER BY clause is used to order the result. Consider the following example.

Example

snippet
import mysql.connector

#Create the connection object 
myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")

#creating the cursor object
cur = myconn.cursor()

try:
    #Reading the Employee data    
    cur.execute("select name, id, salary from Employee order by name")

    #fetching the rows from the cursor object
    result = cur.fetchall()

    print("Name    id    Salary");

    for row in result:
        print("%s    %d    %d"%(row[0],row[1],row[2]))
except:
    myconn.rollback()

myconn.close()

Output:

Output
Name id Salary David 103 25000 John 101 25000 John 102 25000 Mike 105 28000 Nick 104 90000

Order by DESC

This orders the result in the decreasing order of a particular column.

Example

snippet
import mysql.connector

#Create the connection object 
myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")

#creating the cursor object
cur = myconn.cursor()

try:
    #Reading the Employee data    
    cur.execute("select name, id, salary from Employee order by name desc")

    #fetching the rows from the cursor object
    result = cur.fetchall()

    #printing the result
    print("Name    id    Salary");
    for row in result:
        print("%s    %d    %d"%(row[0],row[1],row[2]))

except:
    myconn.rollback()

myconn.close()

Output:

Output
Name id Salary Nick 104 90000 Mike 105 28000 John 101 25000 John 102 25000 David 103 25000
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