Sql 如何解决

我要学习sql，但还没有解决这个问题，有人能帮我吗

展示非优胜者的参赛者

删除所有非优胜者

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谢谢

不在示例中

1. SELECT * FROM runners WHERE id NOT IN (SELECT id_winner FROM races);

2. DELETE FROM runners WHERE id NOT IN (SELECT id_winner FROM races);

不存在这样的例子

1. SELECT * FROM runners a WHERE NOT EXISTS (SELECT 1 FROM races WHERE id_winner = a.id);

2. DELETE a FROM runners a WHERE NOT EXISTS (SELECT 1 FROM races WHERE id_winner = a.id);

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到目前为止，您尝试了哪些查询来解决这个问题？对于空值，NOT in有点危险。是的，他的要求很简单。对于较大的数据集，NOT EXISTS更好。警告是关于空值，而不是数据集的大小。（此外，目前大多数dbms产品都以同样的方式进行优化。）

1. SELECT * FROM runners a WHERE NOT EXISTS (SELECT 1 FROM races WHERE id_winner = a.id);

2. DELETE a FROM runners a WHERE NOT EXISTS (SELECT 1 FROM races WHERE id_winner = a.id);