MYSQLMYSQL

Posted 2020-10-27 jomini

一、检索数据

    1.1、检索单个列  :  

SELECT  prod_name  
FROM products;

    1.2、检索多个列 ：SELECT  prod_id, prod_name，prod_price  FROM products;

SELECT  prod_id, prod_name，prod_price  
FROM products;

    1.3、检索所有列 ：SELECT * FROM products; 

SELECT * 
FROM products; 

    1.4、检索不同的行（如果要输出唯一的结果就要使用，因为SELECT vend_id FROM products;  将会输出重复的结果） ：

                                SELECT DISTINCT vend_id FROM products;  

                               注：如果用DISTINCT关键字加上不同类型的两列，除非两列所有都不同，否则都全输出，相当于失效；

SELECT DISTINCT vend_id 
FROM products;  

    1.5、限制结果:

         (1)返回前5行 ：SELECT prod_name FROM products LIMIT 5; 

SELECT prod_name 
FROM products 
LIMIT 5; 

         (2)返回第5行到其后的五行：SELECT prod_name FROM products LIMIT 5，5； 

SELECT prod_name 
FROM products 
LIMIT 5，5； 

 

                           

二、排序检索数据

      2.1、按单个排序：SELECT prod_name FROM products ORDER BY prod_name    

SELECT prod_name 
FROM products 
ORDER BY prod_name;  

    

      2.2、按多个排序：SELECT prod_id, prod_price, prod_name FROM products ORDER BY prod_name, prod_price; 

SELECT prod_id, prod_price, prod_name 
FROM products 
ORDER BY prod_name, prod_price; 

 

     2.3 降序排序：(1) SELECT prod_id, prod_price, prod_name FROM products ORDER BY prod_price DESC;

SELECT prod_id, prod_price, prod_name 
FROM products 
ORDER BY prod_price DESC;

                         (2) SELECT prod_id, prod_price, prod_name FROM products ORDER BY prod_price DESC, prod_name;  

SELECT prod_id, prod_price, prod_name 
FROM products 
ORDER BY prod_price DESC, prod_name; 

 

三、过滤数据

      3.1、使用WHERE子句：SELECT prod_name, prod_price FROM products WHERE prod_price = 2.50;

SELECT prod_name, prod_price 
FROM products 
WHERE prod_price = 2.50;

      3.2、 使用WHERE子句操作符：

                                             

         3.2.1 (1）检查单个值：SELECT prod_name, prod_price FROM products WHERE prod_name = ‘fuses‘;

SELECT prod_name, prod_price 
FROM products 
WHERE prod_name = ‘fuses‘;

                 (2) SELECT prod_name, prod_price FROM products WHERE prod_price < ‘10;

SELECT prod_name, prod_price 
FROM products 
WHERE prod_price < 10;

          3.2.2 不匹配查询

                  （1）找出不是102供应商供应的货品：SELECT vend_id, prod_name FROM products WHERE vend_id <> 102;

SELECT vend_id, prod_name 
FROM products 
WHERE vend_id <> 102;

         

          3.2.3 范围值查询

                   (1) 查找价格在 5 和 10 之间的货物：

                        SELECT prod_name, prod_price FROM products WHERE prod_price BETWEEN 5 AND 10;

SELECT prod_name, prod_price 
FROM products 
WHERE prod_price 
BETWEEN 5 AND 10;

             

         3.2.4 空值查询

                 查找价格为null 的货物: SELECT prod_name FROM products WHERE prod_price IS NULL;

SELECT prod_name 
FROM products 
WHERE prod_price IS NULL;

 

四、数据过滤、

        4.1