如何使两列无法拥有相同的数据。我的表格由3个字段组成。
studentid id_project level_of_want
1 2 high
1 3 low
1 4 high
1 2 low
我希望一列能够拥有相同的数据(例如 studid 中的第1栏),但 studid 和 /id_project 不能拥有同一数据一次以上(上文目录1和4)。 student 可以是1,而 id_project 可以是1,但只能存在一次。
您需要添加“ 独特” 索引 。
阅读http://dev.mysql.com/doc/refman/5.0/en/capement-index.html
create unique index my_index on my_table (studentid, id_project);
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