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
1. import mysql.connector
2.
3. #Create the connection object
4. myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
5.
6. #creating the cursor object
7. cur = myconn.cursor()
8.
9. try:
10. #Reading the Employee data
11. cur.execute("select * from Employee")
12.
13. #fetching the rows from the cursor object
14. result = cur.fetchall()
15. #printing the result
16.
17. for x in result:
18. print(x);
19. except:
20. myconn.rollback()
21.
22. myconn.close()
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.
How to find Nth Salary in MySQl
Example
1. import mysql.connector
2. #Create the connection object
3. myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
4. #creating the cursor object
5. cur = myconn.cursor()
6. try:
7. #Reading the Employee data
8. cur.execute("select name, id, salary from Employee")
9.
10. #fetching the rows from the cursor object
11. result = cur.fetchall()
12. #printing the result
13. for x in result:
14. print(x);
15. except:
16. myconn.rollback()
17. myconn.close()
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
1. import mysql.connector
2.
3. #Create the connection object
4. myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
5.
6. #creating the cursor object
7. cur = myconn.cursor()
8.
9. try:
10. #Reading the Employee data
11. cur.execute("select name, id, salary from Employee")
12.
13. #fetching the first row from the cursor object
14. result = cur.fetchone()
15.
16. #printing the result
17. print(result)
18.
19. except:
20. myconn.rollback()
21.
22. myconn.close()
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
1. import mysql.connector
2.
3. #Create the connection object
4. myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
5.
6. #creating the cursor object
7. cur = myconn.cursor()
8.
9. try:
10.
11. #Reading the Employee data
12. cur.execute("select name, id, salary from Employee")
13.
14. #fetching the rows from the cursor object
15. result = cur.fetchall()
16.
17. print("Name id Salary");
18. for row in result:
19. print("%s %d %d"%(row[0],row[1],row[2]))
20. except:
21. myconn.rollback()
22.
23. myconn.close()
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
1. import mysql.connector
2.
3. #Create the connection object
4. myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
5.
6. #creating the cursor object
7. cur = myconn.cursor()
8.
9. try:
10. #Reading the Employee data
11. cur.execute("select name, id, salary from Employee where name like 'J%'")
12.
13. #fetching the rows from the cursor object
14. result = cur.fetchall()
15.
16. print("Name id Salary");
17.
18. for row in result:
19. print("%s %d %d"%(row[0],row[1],row[2]))
20. except:
21. myconn.rollback()
22.
23. myconn.close()
Output:
Name id Salary
John 101 25000
John 102 25000
Example: printing the names with id = 101, 102, and 103
1. import mysql.connector
2.
3. #Create the connection object
4. myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
5.
6. #creating the cursor object
7. cur = myconn.cursor()
8.
9. try:
10. #Reading the Employee data
11. cur.execute("select name, id, salary from Employee where id in (101,102,103)")
12.
13. #fetching the rows from the cursor object
14. result = cur.fetchall()
15.
16. print("Name id Salary");
17.
18. for row in result:
19. print("%s %d %d"%(row[0],row[1],row[2]))
20. except:
21. myconn.rollback()
22.
23. myconn.close()
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
1. import mysql.connector
2.
3. #Create the connection object
4. myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
5.
6. #creating the cursor object
7. cur = myconn.cursor()
8.
9. try:
10. #Reading the Employee data
11. cur.execute("select name, id, salary from Employee order by name")
12.
13. #fetching the rows from the cursor object
14. result = cur.fetchall()
15.
16. print("Name id Salary");
17.
18. for row in result:
19. print("%s %d %d"%(row[0],row[1],row[2]))
20. except:
21. myconn.rollback()
22.
23. myconn.close()
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
1. import mysql.connector
2.
3. #Create the connection object
4. myconn = mysql.connector.connect(host = "localhost", user = "root",passwd = "google",database = "PythonDB")
5.
6. #creating the cursor object
7. cur = myconn.cursor()
8.
9. try:
10. #Reading the Employee data
11. cur.execute("select name, id, salary from Employee order by name desc")
12.
13. #fetching the rows from the cursor object
14. result = cur.fetchall()
15.
16. #printing the result
17. print("Name id Salary");
18. for row in result:
19. print("%s %d %d"%(row[0],row[1],row[2]))
20.
21. except:
22. myconn.rollback()
23.
24. myconn.close()
Output:
Name id Salary
Nick 104 90000
Mike 105 28000
John 101 25000
John 102 25000
David 103 25000
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