SQL Exercise: Display Employees whose last name is McEwen

Last update on March 31 2023 06:07:17 (UTC/GMT +8 hours)

SQL SORTING and FILTERING on HR Database: Exercise-3 with Solution

3. From the following table, write a SQL query to find those employees whose last name is "McEwen". Return first name, last name and department ID.

Sample table: employees

Sample Solution:

SELECT first_name, last_name, department_id
 FROM employees
  WHERE last_name = 'McEwen';

Sample Output:

 first_name | last_name | department_id
------------+-----------+---------------
 Allan      | McEwen    |            80
(1 row)

Code Explanation:

The said query in SQL that retrieves first name, last name, and department ID columns from the "employees" table where the last name is 'McEwen'. As a result of the query, all the rows that meet the condition stipulated in the "WHERE" clause will be returned from the 'employees' table.

Relational Algebra Expression:

Relational Algebra Tree:

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Query Visualization:

Duration:

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Previous SQL Exercise: Find those employees who earn more than 8000.
Next SQL Exercise: Details of employees without any department number.

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SQL: Tips of the Day

Difference between natural join and inner join

One significant difference between INNER JOIN and NATURAL JOIN is the number of columns returned-

Consider:

TableA                           TableB
+------------+----------+        +--------------------+    
|Column1     | Column2  |        |Column1  |  Column3 |
+-----------------------+        +--------------------+
| 1          |  2       |        | 1       |   3      |
+------------+----------+        +---------+----------+

The INNER JOIN of TableA and TableB on Column1 will return

SELECT * FROM TableA AS a INNER JOIN TableB AS b USING (Column1);
SELECT * FROM TableA AS a INNER JOIN TableB AS b ON a.Column1 = b.Column1;

+------------+-----------+---------------------+    
| a.Column1  | a.Column2 | b.Column1| b.Column3|
+------------------------+---------------------+
| 1          |  2        | 1        |   3      |
+------------+-----------+----------+----------+

The NATURAL JOIN of TableA and TableB on Column1 will return:

SELECT * FROM TableA NATURAL JOIN TableB
+------------+----------+----------+    
|Column1     | Column2  | Column3  |
+-----------------------+----------+
| 1          |  2       |   3      |
+------------+----------+----------+

Ref: https://bit.ly/3AG5CId

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