SQL And Database:
1.SQL query is to request the data from the database.
2.We use SELECT command to pick the specific column from the database.
SELECT rank,major # This command will return a list which contains the data completely follow the order of column it selected.
FROM recent_grads;
3.Use WHERE command to select certain rows which satisfy the condition.
SELECT Major,Employed FROM recent_grads WHERE Employed > 10000
4.Use LIMIT to specify certain number of results.
5.Use Order by to specify the order for the rows.(desc and asc)
6.Order by can also specify mutiple columns by orders.
原文：http://www.cnblogs.com/kingoscar/p/6076169.html