【SQL必知必会】第4课 过滤数据

#4.1 使用WHERE 子句

1 SELECT prod_name, prod_price
2 FROM Products
3 WHERE prod_price = 3.49;
4
5 /*
6 *** 输出可能不同，有可能是3.49,3.490,3.4900,与数据库存储时的数据类型有关
7 *** where 语句应该在order by 前面;
8 */

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#4.2 WHERE 子句操作符

#4.2.1 检查单个值

1 SELECT prod_name, prod_price
2 FROM Products
3 WHERE prod_price < 10;

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结果

#4.2.2 不匹配检查

1 SELECT vend_id, prod_name
2 FROM Products
3 WHERE vend_id <> 'DLL01';
4
5 /*
6 提示：何时使用单引号?
7 答：当数据列是字符串
8 */

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#4.2.3 范围值检查

1 SELECT prod_name, prod_price
2 FROM Products
3 WHERE prod_price BETWEEN 5 AND 10;
4
5 # [5,10]

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#4.2.4 空值检查

1 SELECT cust_name
2 FROM CUSTOMERS
3 WHERE cust_email IS NULL;

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