Question

我有一张名为Flights的表格。该表具有以下结构：

+----+----------+---------------+
| Id |   Name   | DepartureDate |
+----+----------+---------------+
|  1 | 20130001 | 2013-02-14    |
|  2 | 20130002 | 2013-05-04    |
|  3 | 20140001 | 2014-01-16    |
|  4 | 20130003 | 2013-07-15    |
|  5 | 20150001 | 2015-01-01    |
|  6 | 20150002 | 2015-09-14    |
+----+----------+---------------+

如您所见，航班的名称取决于出发日期的年份和相关数字。

问题在于，当我想插入一个航班时，即2013年，我必须进行SELECT COUNT(*)查询以获取该表中该年度的航班数量，然后制作{{1}声明。我认为这很糟糕且效率低下，因为它可能是重复的航班号。

您建议做什么操作？

Answer 1

如果您正在使用（或可以切换到）MyISAM Engine，您应该使用MySQL的AUTO_INCREMENT。

要观看此工作：http://sqlfiddle.com/#!9/c6af9/1

CREATE TABLE flights (
  year ENUM('2013','2014','2015') NOT NULL,
  id MEDIUMINT NOT NULL AUTO_INCREMENT,
  DepartureDate date NOT NULL,
  PRIMARY KEY (year,id)
) ENGINE=MyISAM;

然后在你之前插入或像这样插入：

INSERT INTO flights (year, DepartureDate) VALUES ('2013', date('2013-07-03')), 
('2014', date('2014-06-03')), ('2013', date('2013-02-06')), 
('2015', date('2015-01-04')), ('2015', date('2015-02-04')),
('2015', date('2015-12-10')), ('2015', date('2015-06-04')),
('2015', date('2015-11-04')), ('2015', date('2015-10-04')),
('2015', date('2015-01-07')), ('2015', date('2015-01-09')),
('2015', date('2015-01-09')), ('2015', date('2015-09-12')),
('2015', date('2015-02-09')), ('2015', date('2015-07-04'));

在寻找记录时，请执行以下操作：

SELECT CONCAT(year, LPAD(id, 4, '0')) AS name, DepartureDate FROM flights;

供进一步参考： http://dev.mysql.com/doc/refman/5.5/en/example-auto-increment.html

Answer 2

我仍然不确定你的目标是什么。

但只是我的猜测：

http://sqlfiddle.com/#!9/8dc5b/1

INSERT INTO flights 
SELECT 7, MAX(Name)+1, @d 
FROM flights
WHERE YEAR(DepartureDate)=YEAR(@d);

或

INSERT INTO flights 
SELECT 7, MAX(Name)+1, date('2013-05-04') 
FROM flights
WHERE YEAR(DepartureDate)=YEAR(date('2013-05-04'));

或者您的id已经是AUTO_INCREMENT：

INSERT INTO flights 
SELECT null, MAX(Name)+1, date('2013-05-04') 
FROM flights
WHERE YEAR(DepartureDate)=YEAR(date('2013-05-04'));

Answer 3

最后，我使用@Alex的建议使用了触发事件。

CREATE TRIGGER `flights_iu_trigger` BEFORE INSERT ON `flights` 
FOR EACH ROW 
BEGIN
    DECLARE flight_name INT;
    SELECT (IFNULL(MAX(Name), CONCAT(YEAR(NEW.DepartureDate),'0000')) + 1) 
    INTO flight_name FROM flights 
    WHERE YEAR(flights.DepartureDate) = YEAR(NEW.DepartureDate); 
    SET NEW.Name = flight_name;
END;

通过这些程序，我会根据出发年份自动设置新航班的名称

在表中插入一个字段，该字段取决于先前设置的值

3 个答案: