SQL必知必会笔记（一）
作者：互联网
SQL必知必会（一）
1，任何人一直学习任何一门手艺都会有些烦躁
2，休息好和玩好是学好的前提
3，死记硬背是融会贯通的前提
基础知识
数据：
数据库：保存有组织的数据的容器（通常是一个文件或一组文件）
表：某种特定类型数据的结构化清单 表名唯一
列
数据类型
行：记录
主键：
外键：
必备代码
#一切以mysql为演示
#切换表
USE dingdan;
#检索单个列
SELECT prod_name FROM products;
#检索多个列
SELECT prod_name,prod_id,prod_price FROM
products;
#检索所有列
SELECT * FROM products;
#只保留不同的值
SELECT DISTINCT vend_id FROM products;
#限制结果(MYSQL)
SELECT prod_name FROM products LIMIT 5; //前5个
SELECT prod_name FROM products LIMIT 3
OFFSET 5; //第三行起的5行数据
#排序数据(单行)
SELECT prod_name FROM products
ORDER BY prod_name;
#排序数据（多行）
SELECT prod_name,prod_id,prod_price
FROM products
ORDER BY prod_id,prod_name;
#排序数据（按照列的位置）
SELECT prod_name,prod_id,prod_price
FROM products
ORDER BY 2,1;
#指定排序方向（降序）
SELECT prod_name,prod_id,prod_price
FROM products
ORDER BY prod_id,prod_name DESC;
#指定排序方向（升序）默认升序
SELECT prod_name FROM products
ORDER BY prod_name ASC;
#过滤数据 =
<> != < > <= >= !< !> between is
null
SELECT prod_name,prod_price
FROM products
WHERE prod_price = 3.49;
#检查单个值
SELECT prod_name,prod_price
FROM products
WHERE prod_price > 3.49;
#不匹配检查
SELECT prod_name,prod_price
FROM products
WHERE prod_price <> 3.49;
#between
SELECT prod_name,prod_price
FROM products
WHERE prod_price BETWEEN 5 AND 10;
#空值检查
SELECT prod_name,prod_price
FROM products
WHERE prod_price IS NULL;
#组合where and
SELECT prod_name,prod_price
FROM products
WHERE prod_price BETWEEN 5 AND 10
AND
WHERE prod_name IS NOT NULL;
#or
SELECT prod_name,prod_price
FROM products
WHERE vend_id = 'DLL01' OR vend_id =
'BRS01';
#SQL优先处理and,再处理or
SELECT prod_name,prod_price
FROM products
WHERE(vend_id = 'DLL01' OR vend_id =
'BRSO1')
AND prod_price >=10;
#IN 操作符
SELECT prod_name,prod_price
FROM products
WHERE vend_id IN ('DLL01','BRS01')
ORDER BY prod_name;
#NOT 否定紧跟的限定语句
SELECT prod_name,prod_price
FROM products
WHERE NOT vend_id = 'DLL01'
ORDER BY prod_name;
#通配符 %
SELECT prod_id,prod_name
FROM Products
WHERE prod_name LIKE 'Fish%';
SELECT prod_id,prod_name
FROM Products
WHERE prod_name LIKE '%bean bag%';
# _ 单个字符
SELECT prod_id,prod_name
FROM Products
WHERE prod_name LIKE '__ inch teddy bear';
#[] 字符集匹配
SELECT cust_contact
FROM Customers
WHERE cust_contact LIKE '[JM]%'
ORDER BY cust_constact;
#[^] 字符集匹配
SELECT cust_contact
FROM Customers
WHERE cust_contact LIKE '[^JM]%'
ORDER BY cust_constact;
#拼接（MySQL）
SELECT CONCAT(vend_name,'
(',vend_country,')')
FROM Vendors
ORDER BY vend_name;
#RTRIM 去除右边空格
#LTRIM 去除左边空格
#TRIM 去除左右空格
SELECT RTRIM（vend_name）+'(' +
RTRIM(vend_country) + ')'
FROM Vendors
ORDER BY vend_name;
#使用别名(MySQL)
SELECT CONCAT(vend_name,'
(',vend_country,')') AS vend_title
FROM Vendors
ORDER BY vend_name;
#执行算术计算
SELECT prod_id,quantity,item_price,
quantity * item_price AS expanded_price
FROM OrderItems
WHERE order_num = 20008;
#函数 UPPER
SELECT vend_name, UPPER(vend_name) AS
vend_name_upcase
FROM Vendors
ORDER BY vend_name;
/*
UPPER()
转换成大写
LOWER() 小写
LEFT()
返回字符串左边的字符
RIGHT() 右
LENGTH()
返回字符串的长度
SOUNDEX() 返回字符串的语音表示的字母数字
*/
#发音匹配
SELECT cust_name,cust)contact
FROM Customers
WHERE SOUNDEX(cust_contact) =
SOUNDEX('Michael Green');
#日期函数（MySql）
SELECT order_num
FROM Orders
WHERE YEAR(order_date) = 2012;
/*
ABS()绝对值
COS()余弦
EXP()指数值
PI()圆周率
SIN()正弦
SQRT()平方根
TAN()正切
AVG()
COUNT()
MAX()
MIN()
SUM()
*/
#AVG()
SELECT AVG(prod_price) AS avg_price
FROM Products
WHERE vend_id = 'DLL01';
#count()
SELECT COUNT(cust_email) AS num_cust
FROM Customers;
#组合聚集函数
SELECT COUNT(*) AS num_items,
MIN(prod_price) AS price_min,
MAX(prod_price) AS price_max,
AVG(prod_price) AS price_avg
FROM Products;
#数据分组
SELECT vend_id,COUNT(*) AS num_prods
FROM Products
GROUP BY vend_id;
#过滤分组
SELECT vend_id,COUNT(*) AS num_prods
FROM Products
GROUP BY vend_id
HAVING COUNT(*) >=2;
今天下午SQL学到这里算是烦躁了，明天加油！
悦悦是个大菜鸟
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标签：name,必知,price,SQL,vend,必会,prod,id,SELECT 来源： https://blog.csdn.net/zhangzhangchenchu/article/details/104100215