Mastering SQL Advanced Commands

What does the DISTINCT keyword do in SQL?

• The DISTINCT keyword limits the number of records returned.

• The DISTINCT keyword combines multiple records into one.

• The DISTINCT keyword sorts the result set alphabetically.

• The DISTINCT keyword removes duplicate records from the result set.

How would you write a query to select unique values from a column named 'city'?

• SELECT UNIQUE city FROM table_name;

• SELECT city FROM table_name WHERE city IS NOT NULL;

• SELECT DISTINCT city FROM table_name;

• SELECT city FROM table_name GROUP BY city;

Which SQL clause is used to filter records based on a condition?

• WHERE

• HAVING

• GROUP BY

• SELECT

How can you combine multiple conditions in a SQL query?

• Use SELECT and FROM clauses to combine conditions.

• Use AND and OR operators to combine conditions.

• Combine conditions by using GROUP BY only.

• Conditions can only be combined in subqueries.

What is the purpose of the ORDER BY clause in SQL?

• To limit the number of rows returned by a query.

• To filter the result set of a query.

• To sort the result set of a query.

• To group the result set of a query.

Write a SQL query to select distinct 'product_name' from 'products' where 'category' is 'electronics'.

• SELECT product_name FROM products WHERE category = 'electronics';

• SELECT DISTINCT product_name FROM products;

• SELECT product_name, category FROM products WHERE category = 'electronics';

• SELECT DISTINCT product_name FROM products WHERE category = 'electronics';

How do you use the AND operator in a SQL WHERE clause?

• Use the OR operator to combine conditions in a WHERE clause.

• The AND operator is used only in SELECT statements.

• Use the AND operator to combine conditions in a WHERE clause, e.g., WHERE condition1 AND condition2.

• You cannot use the AND operator in SQL.

What is the difference between using OR and AND in SQL conditions?

• 'AND' requires at least one condition to be true; 'OR' requires all conditions to be true.

• 'AND' is used for filtering results; 'OR' is used for sorting results.

• 'AND' requires all conditions to be true; 'OR' requires at least one condition to be true.

• 'AND' can only be used with numeric conditions; 'OR' can be used with text conditions.

Write a query to select distinct 'employee_id' from 'employees' where 'department' is 'sales' and 'status' is 'active'.

• SELECT employee_id FROM employees WHERE department = 'sales';

• SELECT DISTINCT employee_id FROM employees WHERE department = 'sales' AND status = 'active';

• SELECT DISTINCT employee_id FROM employees WHERE status = 'active';

• SELECT employee_id, department FROM employees WHERE department = 'sales' AND status = 'inactive';

How would you order the results of a query by 'salary' in descending order?

• GROUP BY salary DESC

• ORDER BY salary ASC

• SORT BY salary DESC

• ORDER BY salary DESC