Cassandra rangequery，知道开始键的开始

问题描述

让我澄清一下

我有一个列族，用UTF8键：apple＃NewYork，banana＃LosAngeles，banana＃NewYork，cherry＃ ...等等。

我需要的是因为它们被排序，然后我想得到所有的香蕉开始键？

$ b $

解决方案

复合类型如何？

将当前行映射到

row_key => {
banana：a =>愿望，
香蕉：b =>您希望的值，
...
}

复合类型的优点

1. 排序时保留类型属性


2. 您的组合键是 a：b：c ，您可以查询a，a：b范围内的所有列，也可以查询如a：b：c

现在您可以执行列切片
例如：

  row_key => {1：a => 1,1：b => 1。 1，10：bb => 1,1：c => 1。 2} 
 ColumnSlice（array（1），array（1））=>第一个组件等于1的所有列
 ColumnSlice（array（1），array（10））=>所有列的第一个组件在1和10之间
 ColumnSlice（，array（1，'c'））=>从第一个组件小于1且第二个组件小于'c'的行开头的所有列
  

你可以做相反的上述事情，也可以玩包容性&排除限制。

还有一点要记住，你不能直接要求第二个组件范围内的所有列< x跳过第一个

偶数行键支持复合类型，但是如果你使用随机分区器，那就没有意义了。

Let me clarify it

I have a Column Family, with UTF8 keys like that :apple#NewYork, banana#LosAngeles, banana#NewYork, cherry#NewYork, ... and so on

I need that because they are sorted, and then I would like to get all 'banana' starting keys?

Is it possible or is there a workaround?

解决方案

How about composite types?

Map your current rows to columns like

row_key => { banana:a => "value you wish", banana:b => "value you wish", ...}

Advantages of composite types are

1. They preserve type property while sorting
2. Incase your composite key is a:b:c you can query for all columns in the range of a, a:b and also point queries like a:b:c

Now you can perform Column Slice for example using phpcassa Ex:

row_key => { 1:a => 1, 1:b => 1, 10:bb => 1, 1:c => 2}
ColumnSlice(array(1), array(1)) => All Columns with first component equal to 1
ColumnSlice(array(1), array(10)) => All Columns with first component between 1 and 10
ColumnSlice("", array(1, 'c')) => All Columns from the beginning of row whose first component less than 1 and second component less than 'c' 

You can do the above said things in reverse and can also play with inclusive & exclusive limits.

Also one point to remember, You can't directly ask for all columns in the range of second component < x skipping the first one

Even row keys support composite types but in case you are using random partitioner then it makes no sense.

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