SQL是目前使用最为广泛的数据库语言之一。这里，我总结了在数据库上，用SQL语言对数据排序、过滤和分组，以及表、视图、联结、子查询、游标、存储过程和触发器等内容。
1.检索数据
SELECT prod_nameFROM Products;
#检索单列
SELECT prod_id, prod_name, prod_priceFROMProducts;
#检索多列
SELECT * FROM Products;
#检索所有列
SELECT DISTINCTvend_id FROMProducts;
#检索不同的值
SELECTprod_name FROM Products LIMIT 5;
#返回不超过5行数据
SELECTprod_name FROM Products LIMIT 5 OFFSET 5;
#返回从第5行起的5行数据。LIMIT指定返回的行数，LIMIT带的OFFSET指定从哪儿开始。
/* SELECT prod_name, vend_id
FROMProducts; */
SELECTprod_name
FROMProducts;
#多行注释
2.排序检索数据
SELECTprod_name
FROMProducts
ORDER BYprod_name;
#排序数据
SELECT prod_id, prod_price, prod_name
FROMProducts
ORDER BY prod_price, prod_name;
#按多个列排序
SELECT prod_id, prod_price, prod_name
FROMProducts
ORDER BY 2, 3;
#按列位置排序，第三行表示先按prod_price, 再按prod_name进行排序
SELECT prod_id, prod_price, prod_name
FROMProducts
ORDER BY prod_priceDESC, prod_name;
#prod_price列以降序排序，而prod_name列（在每个价格内）仍然按标准的升序排序
3.过滤数据
SELECT prod_name, prod_price
FROMProducts
WHERE prod_price< 10;
#检查单个值
SELECT prod_name, prod_price
FROMProducts
WHERE vend_id <> ‘DLL01’;
#不匹配检查
SELECT prod_name, prod_price
FROMProducts
WHERE prod_priceBETWEEN 5 AND 10;
#范围值检查
SELECT cust_name
FROMCUSTOMERS
WHERE cust_emailIS NULL;
#空值检查
4.高级数据过滤
SELECTprod_id, prod_price, prod_name
FROMProducts
WHERE vend_id = ‘DLL01’ANDprod_price <= 4;
#AND操作符
SELECTprod_name, prod_price
FROMProducts
WHEREvend_id=’DLL01’ OR vend_id=’BRS01’;
#OR操作符
SELECTprod_name, prod_price
FROMProducts
WHERE (vend_id = ’DLL01’ORvend_id=’BRS01’)
ANDprod_price >= 10；
#求值顺序 AND的优先级高于OR
SELECTprod_name, prod_price
FROMProducts
WHERE vend_idIN (‘DLL01’,’BRS01’)
ORDER BY prod_name;
#IN操作符
SELECT prod_name
FROMProducts
WHERE NOTvend_id = ‘DLL01’
ORDER BY prod_name;
#NOT 操作符
SELECT prod_name
FROMProducts
WHEREvend_id <> ‘DLL01’
ORDER BY prod_name;
#NOT 操作符
5.通配符进行过滤
SELECT prod_id, prod_name
FROMProducts
WHERE prod_nameLIKE ‘Fish%’;
#%表示任何字符出现任意次数，找出所有以词Fish起头的产品
SELECT prod_id, prod_name
FROMProducts
WHERE prod_nameLIKE ‘%bean bag%’;
#‘%bean bag%’表示匹配任何位置上包含文本bean bag的值，不论它在之前或之后出现什么字符
SELECT prod_name
FROMProducts
WHERE prod_nameLIKE ‘F%y’;
#找出以F起头，以y结尾的所有产品
根据邮件地址的一部分来查找电子邮件，例如WHERE email LIKE ‘b%@forta.com’
WHERE prod_nameLIKE ‘%’; #不会匹配产品名称为NULL的行，其它均可
%代表搜索模式中给定位置的0个、1个或多个字符
下划线的用途与%一样，但它只匹配单个字符，而不是多个字符
SELECT prod_id, prod_name
FROMProducts
WHERE prod_nameLIKE ‘__inchteddy bear’;
#搜索模式要求匹配两个通配符而不是一个
方括号（[]）通配符用来指定一个字符集，它必须匹配指定位置（通配符的位置）的一个字符
SELECT cust_contact
FROMCustomers
WHERE cust_contactLIKE ‘[JM]%’
ORDER BY cust_contact;
#[JM]匹配方括号中任意一个字符，它也只能匹配单个字符，任何多于一个字符的名字都不匹配。[JM]之后的%通配符匹配第一个字符之后的任意数目的字符，返回所需结果。
SELECT cust_contact
FROMCustomers
WHERE cust_contactLIKE ‘[^JM]%’
ORDER BY cust_contact;
#以J和M之外的任意字符起头的任意联系人名
6.创建计算字段
SELECT Concat(vend_name, ‘ (‘, vend_country, ‘)’)
FROMVendors
ORDER BY vend_name;
输出
Bear Emporium(USA)
Bears R Us (USA)
Doll House Inc.(USA)
Fun and Games(England)
SELECT Concat(vend_name, ‘ (‘, vend_country, ‘)’)
ASvend_title
FROMVendors
ORDER BY vend_name; #给拼接而成新字段起了一个名称
SELECT prod_id,
quantity,
item_price,
quantity*item_price AS expanded_price
FROMOrderItems
WHERE order_num = 20008;
#汇总物品的价格
7.使用函数处理数据
SELECT vend_name, UPPER(vend_name)AS vend_name_upcase
FROMVendors
ORDER BY vend_name;
#文本处理函数
SELECT cust_name, cust_contact
FROMCustomers
WHERE SOUNDEX(cust_contact) =SOUNDEX(‘MichaelGreen’);
# SOUNDEX()函数搜索，匹配所有发音类似于Michael Green 的联系名
SELECT order_num
FROMOrders
WHERE YEAR(order_date) = 2012;
#从日期中提取年份
8.数据汇总
SELECT AVG(prod_price)ASavg_price
FROMProducts;
WHERE vend_id = ‘DLL01’;
SELECT COUNT(*)ASnum_cust
FROMCustomers;
#COUNT(*)对表中行的数目进行计数，不管表列中包含的是空值（NULL）还是非空值
SELECT COUNT(cust_email)ASnum_cust
FROMCustomers;
#只对具有电子邮件地址的客户计数
SELECT MAX(prod_price)ASmax_price
FROMProducts;
#返回Products表中最贵物品的价格
SELECT MIN(prod_price)ASmin_price
FROMProducts;
#返回Products表中最便宜物品的价格
SELECT SUM(quantity)ASitems_ordered
FROMOrderItems
WHERE order_num = 20005;
#SUM(quantity)返回订单中所有物品数量之和，WHERE 子句保证只统计某个物品订单中的物品
SELECT SUM(item_price*quantity)AS total_price
FROMOrderItems
WHERE order_num = 20005;
#SUM(item_price*quantity)返回订单中所有物品价钱之和，WHERE子句保证只统计某个物品订单中的物品
SELECT AVG(DISTINCTprod_price)AS avg_price
FROMProducts
WHERE vend_id = ‘DLL01’;
#使用DISTINCT参数，平均值只考虑各个不同的价格
SELECT COUNT(*) AS num_items,
MIN(prod_price)AS price_min,
MAX(prod_price)AS price_max,
AVG(prod_price)AS price_avg
FROMProducts;
#组合聚集函数
9.分组数据
SELECT vend_id,COUNT(*) AS num_prods
FROMProducts
GROUP BY vend_id;
#创建分组
SELECT vend_id,COUNT(*) AS num_prods
FROMProducts
WHERE prod_price >= 4
GROUP BY vend_id
HAVING COUNT(*) >= 2;
#WHERE 子句过滤所有prod_price至少为4的行，然后按vend_id分组数据，HAVING子句过滤计数为2或2以上的分组。
SELECT order_num,COUNT(*) AS items
FROMOrderItems
GROUP BY order_num
HAVING COUNT(*) >= 3
ORDER BY items, order_num;
#按订购物品的数目排序输出
10.使用子查询
SELECT cust_id
FROMOrders
WHERE order_numIN (SELECT order_num
FROM OrderItems
WHERE prod_id = ‘RGAN01’);
SELECT cust_name, cust_contact
FROMCustomers
WHERE cust_idIN (‘10000000004’, ‘10000000005’);
11.联结表
SELECT vend_name, prod_name, prod_price
FROMVendors, Products
WHERE Vendors vend_id = Products.vend_id;
#创建联结
SELECT vend_name, prod_name, prod_price
FROMVendorsINNER JOIN Products
ONVendors.vend_id = Products.vend_id;
#内联结
SELECT prod_name, vend_name, prod_price, quantity
FROMOrderItems, Products, Vendors
WHERE Products.vend_id = Vendors.vend_id
ANDOrderItems.prod_id = Products.prod_id
ANDorder_num = 20007;
#联结多个表
12.创建高级联结
SELECT c1.cust_id, c1.cust_name, c1.cust_contact
FROMCustomersAS c1, Customers AS c2
WHERE c1.cust_name = c2.cust_name
ANDc2.cust_contact = ‘Jim Jones’;
#自联结，此查询中需要的两个表实际上是相同的表
SELECT C. *, O.order_num, O.order_date,
OI.prod_id, OI.quantity, OI.item_price
FROMCustomersAS C, Orders AS O, OrderItems AS OI
WHERE C.cust_id = O.cust_id
ANDOI.order_num = O.order_num
ANDprod_id = ‘RGAN01’;
#自然联结排除多次出现，使每一列只返回一次
SELECT Customers.cust_id, Orders.order_num
FROMCustomersLEFT OUTER JOIN Orders
ONCustomers.cust_id = Orders.cust_id;
#从FROM子句左边的表Customers表中选择所有行
SELECT Customers.cust_id, Orders.order_num
FROMCustomersRIGHT OUTER JOIN Orders
ONOrders.cust_id =Customers.cust_id;
#从右边的表中选择所有行。
SELECT Customers.cust_id, Orders.order_num
FROMOrdersFULL OUTER JOIN Customers
ONOrders.cust_id = Customers.cust_id;
#检索两个表中的所有行并关联那些可以关联的行
13.组合查询
SELECT cust_name, cust_contact, cust_email
FROMCustomers
WHERE cust_state IN (‘IL’, ‘IN’, ‘MI’)
UNION
SELECT cust_name, cust_contact, cust_email
FROMCustomers
WHERE cust_name = ‘Fun4ALL’
ORDER BY cust_name, cust_contact;
#SQL允许执行多个查询，并将结果作为一个查询结果集返回
14.插入数据
INSERT INTO Customers(cust_id,
Cust_name,
Cust_address,
Cust_city,
Cust_state,
Cust_zip,
Cust_country,
Cust_contact,
Cust_email)
VALUES(‘100000000006’,
‘Toy Land’,
‘123 Any Street’,
‘New York’,
‘NY’,
‘111111’,
‘USA’,
NULL,
NULL);
#插入完整的行
INSERT INTO Customers(cust_id,
Cust_contact,
Cust_email,
Cust_name,
Cust_address,
Cust_city,
Cust_state,
Cust_zip,
Cust_country)
SELECT cust_id,
Cust_contact,
Cust_email,
Cust_name,
Cust_address,
Cust_city,
Cust_state,
Cust_zip,
Cust_country
FROMCustNew；
#将另一个表中的顾客列合并到Customers表中。
SELECT *
INTOCustCopy
FROMCustomers;
#从一个表复制到另一个表中
15.更新和删除数据
UPDATE Customers
SETcust_contact = ‘Sam Roberts’,
Cust_email = ‘[email protected]’
WHERE cust_id = ‘100000000000006’;
#更新多个列
UPDATE Customers
SETcust_email = NULL
WHERE cust_id = ‘1000000005’;
#删除某个列
DELETE FROM Customers
WHERE cust_id = ‘1000000006’;
#删除数据
16. 创建和操纵表
CREATE TABLE OrderItems
(
Order_num INTEGER NOT NULL,
Order_item INTEGER NOT NULL,
Prod_id CHAR(10) NOT NULL,
Quantity INTEGER NOT NULL DEFAULT 1,
Item_price DECIMAL(8, 2) NOT NULL
);
ALTER TABLE Vendors
ADDvend_phone CHAR(20);
#给表增加一个名为vend_phone的列，其数据类型为CHAR
ALTER TABLE Vendors
DROP COLUMN vend_phone;
#该表中的某列
DROP TABLE CustCopy;
#删除表
17.高级SQL特性
主键：表中一列（或多个列）的值唯一标识表中的每一行。主键是一种特殊的约束，用来保证一列或一组列的值唯一标识表中的每一行。这方便直接或交互地处理表中的行。没有主键，要安全地UPDATE 或DELETE特定行而不影响其他行会非常困难。
①任意两行的主键值都不相同；
②每行都具有一个主键值（即列中不允许NULL值）
③包含主键值的列从不修改或更新。
④主键值不能重用
CREATE TABLE Vendors
(
Vend_id CHAR(10) NOT NULL PRIMARYKEY,
Vend_name CHAR(50) NOT NULL,
Vend_address CHAR(50) NULL,
Vend_city CHAR(5) NULL,
Vend_state CHAR(10) NULL,
Vend_zip CHAR(10) NULL,
Vend_country CHAR(50) NULL
);
ALTER TABLE Vendors
ADD CONSTRAINT PRIMARY KEY (vend_id);
#给表vend_id 列定义添加关键字PRIMARYKEY, 使其成为主键转自：https://blog.csdn.net/American199062/article/details/51471769