一级索引和二级索引到底有什么区别?

2021-12-21 00:00:00 indexing database mysql oracle

谁能告诉我主索引和主索引之间的确切区别是什么?二级指标?属于主要类别的不同索引是什么?二级索引?以及使用主索引相对于二级索引的优势是什么?反之亦然?

Can any one tell me what's the exact difference between Primary index & Secondary index? What are the different indexes that comes under category of primary & secondary index? And what's advantages of using primary index over secondary index & vice versa?

推荐答案

主索引:

主索引是一组字段的索引,包括字段的唯一主键,并保证不包含重复项.也称为聚集索引.例如.员工 ID 可以是它的示例.

A primary index is an index on a set of fields that includes the unique primary key for the field and is guaranteed not to contain duplicates. Also Called a Clustered index. eg. Employee ID can be Example of it.

二级索引:

二级索引是一个非主索引并且可能有重复的索引.例如.员工姓名就是一个例子.因为员工姓名可以有相似的值.

A Secondary index is an index that is not a primary index and may have duplicates. eg. Employee name can be example of it. Because Employee name can have similar values.

主索引包含表的关键字段.当表被激活时,主索引会自动在数据库中创建.如果一个大表被频繁访问以至于无法应用主索引排序,你应该为该表创建二级索引.

The primary index contains the key fields of the table. The primary index is automatically created in the database when the table is activated. If a large table is frequently accessed such that it is not possible to apply primary index sorting, you should create secondary indexes for the table.

表上的索引具有三个字符的索引 ID.'0' 为主索引保留.客户可以在 SAP 表上创建自己的索引;他们的 ID 必须以 Y 或 Z 开头.

The indexes on a table have a three-character index ID. '0' is reserved for the primary index. Customers can create their own indexes on SAP tables; their IDs must begin with Y or Z.

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