在 AWS DynamoDb 上查询 Range 键的最大值 [英] Querying for greatest value of Range key on AWS DynamoDb

问题描述

什么是 DynamoDB 等价物

What is the DynamoDB equivalent of

SELECT MAX(RANGE_KEY) FROM MYTABLE WHERE PRIMARYKEY = "value"

我能想到的最好的是

from boto.dynamodb2.table import Table as awsTable

tb = awsTable("MYTABLE")
rs = list(tb.query_2(PRIMARYKEY__eq="value", reverse=True, limit=1))
MAXVALUE = rs[0][RANGE_KEY]

有没有更好的方法来做到这一点?

Is there a better way to do this?

推荐答案

这是正确的方法.

因为Hash Key匹配的记录是按照Range Key排序的，所以按照后代顺序获取第一个会得到最大范围key的记录.

Because the records matched by the Hash Key are sorted by the Range Key, getting the first one by the descendant order will give you the record with the maximum range key.

查询结果始终按范围键排序.如果数据类型为range键为Number，结果按数字顺序返回；否则，结果按 ASCII 字符码的顺序返回价值观.默认情况下，排序顺序是升序.颠倒顺序使用设置为 false 的 ScanIndexForward 参数.

Query results are always sorted by the range key. If the data type of the range key is Number, the results are returned in numeric order; otherwise, the results are returned in order of ASCII character code values. By default, the sort order is ascending. To reverse the order use the ScanIndexForward parameter set to false.

查询和扫描操作 - Amazon DynamoDB:http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/QueryAndScan.html

Query and Scan Operations - Amazon DynamoDB : http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/QueryAndScan.html

注意:通过 boto API 将 reverse 参数设置为 true 等效于通过原生 AWS API 将 ScanIndexForward 设置为 false.

NOTE: Setting the reverse parameter to true via boto API is equivalent to setting ScanIndexForward to false via the native AWS API.

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