useful mysql sql

\c cancel current sql
\q quit mysql command shell

mysql> select 'a' union select 3;
+---+
| a |
+---+
| a |
| 3 |
+---+
2 rows in set (0.29 sec)

SQL Transaction in Rails

http://snippets.dzone.com:80/posts/show/3995

def fetch_value
 sql = ActiveRecord::Base.connection();
 sql.execute "SET autocommit=0";
 sql.begin_db_transaction
 id, value =
 sql.execute("SELECT id, value FROM sometable WHERE used=0 LIMIT 1 FOR UPDATE").fetch_row;
 sql.update "UPDATE sometable SET used=1 WHERE id=#{id}";
 sql.commit_db_transaction
 
 value;
end