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SQL Exercise: Employees whose first or last name begins with D

SQL SORTING and FILTERING on HR Database: Exercise-36 with Solution

36. From the following table, write a SQL query to find the employees whose first or last name begins with 'D'. Return first name, last name.

Sample table : employees


Sample Solution: 

SELECT first_name, last_name 
	FROM employees 
		WHERE  first_name  LIKE 'D%' 
			OR last_name LIKE 'D%';

Sample Output:

 first_name | last_name
------------+-----------
 Lex        | De Haan
 David      | Austin
 Diana      | Lorentz
 Daniel     | Faviet
 Den        | Raphaely
 Curtis     | Davies
 David      | Bernstein
 Louise     | Doran
 Danielle   | Greene
 David      | Lee
 Julia      | Dellinger
 Jennifer   | Dilly
 Donald     | OConnell
 Douglas    | Grant
(14 rows)

Code Explanation:

The said query in SQL which selects the "first_name" and "last_name" columns from the 'employees' table where the "first_name" column starts with the letter 'D' (specified using the "LIKE" operator with the pattern 'D%') or the "last_name" column starts with the letter 'D' (specified using the "LIKE" operator with the pattern 'D%').

Relational Algebra Expression:

Relational Algebra Expression: Display all those employees whose first name or last name starts with the letter D.

Relational Algebra Tree:

Relational Algebra Tree: Display all those employees whose first name or last name starts with the letter D.

Practice Online


HR database model

Query Visualization:

Duration:

Query visualization of Display all those employees whose first name or last name starts with the letter D - Duration

Rows:

Query visualization of Display all those employees whose first name or last name starts with the letter D - Rows

Cost:

Query visualization of Display all those employees whose first name or last name starts with the letter D - Cost

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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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