php查询mysql中某id数据是否存在
php查询mysql中某id数据是否存在的方法：首先创建一个方法function来调用；然后写sql语句，查询对应id的数据；接着调用查询数据库的方法；最后判断返回来的结果是否为空即可。
php查询mysql中某id数据是否存在？
我们可以创建一个方法function来供调用。
方法里先判断id是否为0，为0则肯定是不存在这条数据的。（假设判断数据库的数据是否存在相同id的数据）
然后写sql语句，只能查询对应id的数据是否存在就行了。
然后调用查询数据库的方法，判断返回来的结果是否为空。不为空则是数据已存在。
如果是判断数据是否存在的关键字段是字符串的，我们稍为改一下代码就行了，比如这里的，判断email是否已经存在于数据库中。
我们这里的queryFirstColumn方法是封装好的数据库函数。
也可以将其改成一般的mysql_query的系统内置方法来查询的，代码如图。
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