Question

嗨，你们做了一些更多的修改，如何做到以下几点：

删除属于“A Wilks”的甲壳虫

person (driver-id, name, address)
car (license, model, year)
accident (report-number, date, location)
owns (driver-id, license) 
participated (driver-id, car, report-number, damage-amount)

这是我想出的：

DELETE FROM car
WHERE model = 'beetle'

然而我知道这是错误的，因为它会删除所有的甲壳虫汽车，而不仅仅是A Wilks所拥有的汽车。

Answer 1

DELETE FROM car
WHERE model = 'beetle'
AND license = (
    SELECT o.license from owns o INNER JOIN person p
    ON o.driver-id = p.driver-id
    WHERE p.name = 'A Wilks'
)

Answer 2

DELETE FROM car
WHERE model = 'Beetle' AND license IN (
  SELECT license
  FROM owns
  INNER JOIN Person ON owns.driver_id = person.driver_id
  WHERE person_name = 'A Wilks'

如果您确定只有一个甲壳虫属于“A Wilks”，您可以在查询的第二行使用license =代替license IN。

请考虑坐下来复制MySQL并尝试一些查询;你会更好地学习这些材料：）

Answer 3

DELETE FROM car 
USING car 
INNER JOIN owns 
INNER JOIN person
WHERE car.license=owns.license 
AND car.model='Beetle'
AND owns.driver-id=person.driver-id 
AND person.name='A Wilks';

http://dev.mysql.com/doc/refman/5.0/en///delete.html

Answer 4

delete from car where model ='beetle' and licence=(select licence owns INNER JOIN Person ON owns.driver_id = person.driver_id WHERE person_name = 'A Wilks')

Answer 5

Philippinedev给出的答案很好，我想说明为什么它比使用子查询的答案更好。

他的回答使用了连接语法（最佳性能和控制）：

DELETE FROM car 
USING car 
INNER JOIN owns 
INNER JOIN person
WHERE car.license=owns.license 
AND car.model='Beetle'
AND owns.driver-id=person.driver-id 
AND person.name='A Wilks';

他正在使用对连接表执行查询的语法，并从DELETE FROM子句中删除表中的所有匹配记录。替代方法使用子查询格式（易于编码，性能较差）：

DELETE FROM car
WHERE model = 'beetle'
AND license = (
    SELECT o.license from owns o INNER JOIN person p
    ON o.driver-id = p.driver-id
    WHERE p.name = 'A Wilks'
)

子查询的性能比直接连接更昂贵。如果这是在真实的机动车系统系统上运行的查询（具有数百万条记录），您可能希望不惜一切代价避免使用子查询，而是使用直接连接。

Answer 6

我建议您将所有者添加到汽车并执行：

DELETE FROM car
WHERE model = 'beetle' and owner = 'ownername'

除非您owner中包含car，否则无效。

MYSQL删除记录

6 个答案: