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对于结合唯一的疑惑

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Release： 2016-06-13 12:04:32
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对于组合唯一的疑惑

<br />create table `table` if not exists{<br />  `a` varchar(30) not null<br />  `b` tinyint(1) not null default 0<br />}<br />
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这两个字段一定不能同时重复，故我设置了组合唯一。
现在问题来了，因为每次插入数据时，·a·有可能为空，那就会导致第二条·a·为空的数据因为重复而无法插入。
请教大家有什么解决方法吗？是否只能把`a`设为null？
------解决方案--------------------
a 为空时， b 总有值吧？
------解决方案--------------------
你a字段可能為空，B恆等於0，邏輯上就已經是有問題了。
已經不是組合唯一了，因為B恆等。然後a如果是空就重複了。

Related labels：
nbsp NOT null table varchar
source：php.cn
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