W3. SQL Comments

Question 1

Q: What is the purpose of comments in SQL?

Answer 1

A: Comments explain sections of SQL statements or prevent execution of specific code parts.

Question 2

Q: Are comments supported in Microsoft Access databases?

Answer 2

A: No, comments are not supported in Microsoft Access databases.

Question 3

Q: How do you write a single-line comment in SQL?

Answer 3

A: Use –, followed by the comment text.

Question 4

Q: Write a single-line comment to explain “Select all” before a SQL query.

Answer 4

– Select all:
SELECT * FROM Customers;

Question 5

Q: How can you use a single-line comment to ignore part of a SQL statement?

Answer 5

A: Place – after the code you want to execute, e.g.,

SELECT * FROM Customers – WHERE City=’Berlin’;

Question 6

Q: How do you write a multi-line comment in SQL?

Answer 6

A: Wrap the text with /* and */.

Question 7

Q: Write a multi-line comment to describe a SQL query that selects all records from Customers.

Answer 7

/*
Select all the columns
of all the records
in the Customers table:
*/
SELECT * FROM Customers;

Question 8

Q: How can you use multi-line comments to ignore multiple SQL statements?

Answer 8

A: Place /* before and */ after the statements, e.g.,

/*
SELECT * FROM Customers;
SELECT * FROM Products;
*/

Question 9

Q: Write a query that uses a comment to ignore part of a line in a SELECT statement.

Answer 9

SELECT CustomerName, /City,/ Country FROM Customers;

Question 10

Q: Write a query that uses a comment to ignore part of a condition in a WHERE clause.

Answer 10

SELECT * FROM Customers
WHERE (CustomerName LIKE ‘L%’
OR CustomerName LIKE ‘R%’ /* OR CustomerName LIKE ‘S%’
OR CustomerName LIKE ‘T%’ */
OR CustomerName LIKE ‘W%’)
AND Country=’USA’
ORDER BY CustomerName;