Flash cards
Review the key moves
What is the main idea behind SQL Comments?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
-- ___ all GermanPut the learning moves in the order that makes the concept easiest to apply.
Comments are used to explain SQL code, or to temporarily prevent execution of SQL code (for debugging).
Comments are ignored by the database engine.
SQL supports single-line comments -- , and multi-line comments /* */ .
Note
Comments are not supported in Microsoft Access databases.
SQL Single-line Comments
Single-line comments start with -- and continue to the end of line.
Any text after -- and to the end of the line will be ignored.
The following example uses a single-line comment as an explanation:
Example
-- Selects all German
customers
SELECT * FROM Customers
WHERE Country = 'Germany';The following example uses a single-line comment to comment away the end of a line:
Example
SELECT * FROM Customers -- WHERE City='Berlin';The following example uses a single-line comment to temporarily prevent execution of an SQL statement:
Example
-- SELECT * FROM Customers;
SELECT * FROM Products;SQL Multi-line Comments
Multi-line comments start with /* and end with */ .
Any text between /* and */ will be ignored.
The following example uses a multi-line comment as an explanation:
Example
/* Selects all German customers
from Berlin */
SELECT * FROM Customers
WHERE Country = 'Germany' AND City = 'Berlin';The following example uses a multi-line comment to ignore many SQL statements:
Example
/* SELECT * FROM Customers;
SELECT * FROM Products;
SELECT * FROM Orders;
SELECT * FROM Categories; */
SELECT * FROM Suppliers;To ignore just a part of an SQL code, you can also use multi-line comment:
Example
SELECT CustomerName, /*City,*/ Country FROM Customers;The following example uses a multi-line comment to ignore part of an SQL statement:
Example
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;