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

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

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

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

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

Output:

Name    id    Salary
John    101    25000
John    102    25000

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

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

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

Output:

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