How To Give a User Read-Only Access to a Database? - MySQL FAQs - Managing User Accounts and Access Privileges

If you want give a user read-only access to a database, you can grant to him/her only the "SELECT" privilege, so that he/she can not run any DDL statements, and any INSERT, UPDATE, or DELETE statements. The tutorial exercise gives you a good example:

>cd \mysql\bin
>mysql -u root -pretneciyf

mysql> USE fyi;
Database changed

mysql> CREATE TABLE links (id INTEGER, name VARCHAR(80));
Query OK, 0 rows affected (0.14 sec)

mysql> INSERT INTO links VALUES (1, 'dba.fyicenter.com');
Query OK, 1 row affected (0.05 sec)

mysql> CREATE USER guest IDENTIFIED BY 'pub';
Query OK, 0 rows affected (0.24 sec)

mysql> GRANT SELECT ON fyi.* TO guest;
Query OK, 0 rows affected (0.00 sec)

mysql> QUIT;

>mysql -u guest -ppub

mysql> use fyi;
Database changed

mysql> SELECT * FROM links;
+------+-------------------+
| id   | name              |
+------+-------------------+
|    1 | dba.fyicenter.com |
+------+-------------------+
1 row in set (0.04 sec)

mysql> INSERT INTO links VALUES (2, 'dev.fyicenter.com');
ERROR 1142 (42000): INSERT command denied to user 
 'guest'@'localhost' for table 'links'