MySQL Comments
Comments are used to explain SQL code, or to temporarily prevent execution of SQL code (for debugging).
Comments are ignored by the database engine.
MySQL supports single-line comments --, and multi-line comments /* */.
Note: MySQL requires a space after the second dash in a single-line comment!
MySQL 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;
MySQL 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;
