Index (RedkaleProject 2.8.0-SNAPSHOT API)

```
@Documented
@Target(TYPE)
@Retention(RUNTIME)
public @interface Index
```
Used in schema generation to specify creation of an index.
Note that it is not necessary to specify an index for a primary key, as the primary key index will be created automatically.
The syntax of the columnList element is a column_list, as follows:
```
    column::= index_column [,index_column]*
    index_column::= column_name [ASC | DESC]
 
```
If ASC or DESC is not specified, ASC (ascending order) is assumed.
从以下版本开始:

Java Persistence 2.1

必需元素概要

所需元素
修饰符和类型必需的元素说明

String[] columns
(Required) The names of the columns to be included in the index, in order.

可选元素概要

可选元素
修饰符和类型	可选元素	说明
`String`	`name`	(Optional) The name of the index; defaults to a provider-generated name.
`boolean`	`unique`	(Optional) Whether the index is unique.

- 元素详细资料
  - columns
```
String[] columns
```
    (Required) The names of the columns to be included in the index, in order.
    
    返回:
    
    String[]
- - name
```
String name
```
    (Optional) The name of the index; defaults to a provider-generated name.
    
    返回:
    
    String
    
    默认值:
    
    ""
- - unique
```
boolean unique
```
    (Optional) Whether the index is unique.
    
    返回:
    
    boolean
    
    默认值:
    
    false