一、语句

1、USE + 库名   ：所选库名加粗

2、SELECT语句

SELECT + 字段名 AS + 字段别名 FROM + 表名 WHERE + 条件  ORDER BY + 字段名

DISTINCT ：去重        
ORDER BY ：排序
字段名可以使用 （  +   -  *   /  ）得到新的字段
字段名 + AS + 字段别名

eg:

SELECT DISTINCT
    last_name,
    first_name AS 'first name',
    points,
    points + 10 * 100  AS discount_factor
FROM customers
ORDER BY last_name

3、WHERE语句

SELECT * FROM Customers WHERE points > 3000

SELECT * FROM Customers WHERE state = 'VA'

SELECT * FROM Customers WHERE state <> 'VA'

SELECT * FROM Customers WHERE DATA > '1999-12-01'

SELECT * FROM Customers WHERE DATA > '1999-12-01' AND points > 1000

SELECT * FROM Customers WHERE NOT DATA > '1999-12-01' AND points > 1000

我们可以用 > >= < <= = != <>
<>表示不等于
条件是字符串的要加''
AND 后加另一个条件 并且两个条件都成立
OR  后加另一个条件 并且两个条件成立一个就可以
AND 优先执行于 OR
NOT 用来否定一个条件