Oracle 横表和纵表
前一段时间了解到的，今天有空写下，备忘~
先来说说横表和纵坐表的概念,先来看看以下两图：
第一张图就是横表，一行表示了一个实体记录，这就是我们传统的设计表的形式
第二张图就是纵表，他的一行记录，是用于表示某个学生的属性名和属性值对应关系，像这边有两个属性（名字和性别），在纵表中就要用两条记录来表示一个学生。
从上面可以观察出，横表的好处是清晰可见，一目了然，但是有一个弊端，如果现在要把这个表加一个字段，那么就必须重建表结构。对于这种情况，在纵表中只需要添加一条记录，就可以添加一个字段，所消耗的代价远比横表小，但是纵表的对于数据描述不是很清晰，而且会造成数据库数量很多，两者利弊在于此。所以，应该把不容易改动表结构的设计成横表，把容易经常改动不确定的表结构设计成纵表。
在实际开发中，经常需要互相转换横表和纵表的形式，这里贴个从纵表数据转成横表显示的形式。
Select student_no,
max(decode(field_name,'student_name',field_value)) As student_name,
max(decode(field_name,'student_sex',field_value )) As student_sex
From cuc_student_y Group By student_no;
横转纵暂时不知~~望高人指点~~
2024年1月26日 20:44
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