SQL Exercises: Select all columns that satisfy a specific condition

Last update on February 10 2025 06:29:21 (UTC/GMT +8 hours)

From the following table, write a SQL query to find customers whose grade is 200. Return customer_id, cust_name, city, grade, salesman_id.

Sample table: customer

 customer_id |   cust_name    |    city    | grade | salesman_id 
-------------+----------------+------------+-------+-------------
        3002 | Nick Rimando   | New York   |   100 |        5001
        3007 | Brad Davis     | New York   |   200 |        5001
        3005 | Graham Zusi    | California |   200 |        5002
        3008 | Julian Green   | London     |   300 |        5002
        3004 | Fabian Johnson | Paris      |   300 |        5006
        3009 | Geoff Cameron  | Berlin     |   100 |        5003
        3003 | Jozy Altidor   | Moscow     |   200 |        5007
        3001 | Brad Guzan     | London     |       |        5005

Sample Solution:

-- This query selects all columns from the 'customer' table.
SELECT *
-- Specifies the table from which to retrieve the data (in this case, 'customer').
FROM customer
-- Filters the rows to only include those where the 'grade' column has the value 200.
WHERE grade = 200;

Output of the Query:

customer_id	cust_name	 city	    grade	salesman_id
3007		Brad Davis	New York	200		5001
3005		Graham Zusi	California	200		5002
3003		Jozy Altidor    Moscow		200		5007

Code Explanation:

The said SQL query that selects all columns from the 'customer' table where the value of "grade" column is 200. The WHERE clause is used to filter the rows and only return the rows that match the condition specified in the WHERE clause.
For this case, it will return all columns of the rows from the 'customer' table with "grade" 200.

Relational Algebra Expression:

Relational Algebra Tree:

Explanation :

Visual presentation :

Practice Online

For more Practice: Solve these Related Problems:

• Write a SQL query to find customers whose grade is 300.
• Write a SQL query to locate employees with a salary greater than 5000.
• Write a SQL query to retrieve products with a stock quantity less than 100.
• Write a SQL query to identify suppliers with a rating of 4 or higher.

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