create table if not exists Person_182 (
    Id int(10) not null auto_increment,
    Email varchar(20) default null,
    primary key(Id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8

insert into Person_182(Email) values ('[email protected]');
insert into Person_182(Email) values ('[email protected]');
insert
 
 into Person_182(Email) values ('[email protected]');
insert into Person_182(Email) values ('[email protected]');
insert into Person_182(Email) values ('[email protected]');
insert into Person_182(Email) values ('[email protected]');

select * from Person_182 order by Email;

2。答案
說明：提交時需要將Person_182修改為Person

SELECT Email 
FROM Person_182
GROUP BY Email 
HAVING COUNT(*) > 1;

SELECT Email 
FROM Person_182
GROUP BY Email 
HAVING COUNT(Id) > 1;

SELECT Email 
FROM Person_182
GROUP BY Email 
HAVING COUNT(Email) > 1;

SELECT distinct a.Email
FROM Person_182 a,Person_182 b
WHERE a.Id > b.Id
AND
 
 a.Email=b.Email

#Use self join
SELECT DISTINCT a.Email
 FROM Person_182 a JOIN Person_182 b
 ON (a.Email = b.Email)
 WHERE a.Id <> b.Id

 SELECT DISTINCT a.Email
 FROM Person_182 a
 WHERE EXISTS(
     SELECT 1
     FROM Person_182 b
     WHERE a.Email = b.Email
     LIMIT 1, 1
 )

練習

建立熟悉的訂單表

create table if not exists Orders (
    O_Id int(10) not null auto_increment,
    OrderDate date default null,
    OrderPrice int(20),
    Customer varchar(20) default null,
    primary key(O_Id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8

insert into Orders(OrderDate, OrderPrice, Customer) values ('2008/12/29', 1000, 'Bush');
insert into Orders(OrderDate, OrderPrice, Customer) values ('2008/12/29', 1600, 'Carter');
insert into Orders(OrderDate, OrderPrice, Customer) values ('2008/12/29', 700, 'Bush');
insert into Orders(OrderDate, OrderPrice, Customer) values ('2008/12/29', 300, 'Bush');
insert into Orders(OrderDate, OrderPrice, Customer) values ('2008/12/29', 2000, 'Adams');
insert into Orders(OrderDate, OrderPrice, Customer) values ('2008/12/29', 100, 'Carter');

select * from Orders order by Customer;

需求1：我們希望查詢每個客戶的總金額（總訂單）。我們想要使用 GROUP BY 語句對客戶進行組合。

SELECT Customer,SUM(OrderPrice) 
FROM Orders
GROUP BY Customer

需求2：我們希望查詢訂單總金額少於 2000 的客戶。
在 SQL 中增加 HAVING 子句原因是，WHERE 關鍵字無法與合計函式一起使用。

SELECT Customer,SUM(OrderPrice) 
FROM Orders
GROUP BY Customer
HAVING SUM(OrderPrice)<2000

需求3：希望查詢客戶 “Bush” 或 “Adams” 擁有超過 1500 的訂單總金額。
我們在 SQL 語句中增加了一個普通的 WHERE 子句：

SELECT Customer,SUM(OrderPrice) 
FROM Orders
WHERE Customer='Bush' OR Customer='Adams'
GROUP BY Customer
HAVING SUM(OrderPrice)>1500

需求4：將Orders表按照OrderPrice降序（升序）後選擇前5個元素？

select * from Orders order by OrderPrice asc limit 5;
select * from Orders order by OrderPrice desc limit 5;

需求5：將將Orders表按照OrderPrice降序後從第3條記錄開始選擇4條記錄？

select * from Orders order by OrderPrice asc limit 2, 4

解釋：
我們知道，在ms sql server中或access中，
若要查詢前10條記錄，使用top 10即可，
但在mysql中不支援這個寫法，它用limit 10。
我們可以利用MySQL中SELECT支援的一個子句——LIMIT——來完成這項功能。
LIMIT可以實現top N查詢，也可以實現M至N（某一段）的記錄查詢，具體語法如下：

SELECT * FROM MYTABLE
ORDER BY AFIELD 
LIMIT offset, recnum
其中offset為從第幾條（M+1）記錄開始，recnum為返回的記錄條數。例： 
select * from mytable
order by afield 
limit 2, 5 
即意為從第3條記錄開始的5條記錄。

參考文章

建立預設的日期時間型別。
OrderDate datetime NOT NULL DEFAULT NOW(),

CREATE TABLE OrdersTestxx
(
    OrderId int NOT NULL auto_increment,
    ProductName varchar(50) NOT NULL,
    OrderDate datetime NOT NULL DEFAULT NOW(),
    PRIMARY KEY (OrderId)
)