使用PHP在AWS DynamoDB中使用JOIN查询

Question

I am currently using MySQL as database for my application in PHP. But now need to migrate to AWS DynamoDB. As I am new to DynamoDB, can anyone help me using JOIN in DynamoDB?

As per my finding, I have found that, JOINs can be used using Hive and Amazon EMR. But here also there is a problem that no resource is available for using Hive with PHP.

Answer 1

hi maybe you can try this

To join two DynamoDB tables The join is computed on the cluster and returned. The join does not take place in DynamoDB. This example returns a list of customers and their purchases for customers that have placed more than two orders.

CREATE EXTERNAL TABLE hive_purchases(customerId bigint, total_cost double, items_purchased array<String>) 
STORED BY 'org.apache.hadoop.hive.dynamodb.DynamoDBStorageHandler'
TBLPROPERTIES ("dynamodb.table.name" = "Purchases",
"dynamodb.column.mapping" = "customerId:CustomerId,total_cost:Cost,items_purchased:Items");

CREATE EXTERNAL TABLE hive_customers(customerId bigint, customerName string, customerAddress array<String>) 
STORED BY 'org.apache.hadoop.hive.dynamodb.DynamoDBStorageHandler'
TBLPROPERTIES ("dynamodb.table.name" = "Customers",
"dynamodb.column.mapping" = "customerId:CustomerId,customerName:Name,customerAddress:Address");

Select c.customerId, c.customerName, count(*) as count from hive_customers c 
JOIN hive_purchases p ON c.customerId=p.customerId 
GROUP BY c.customerId, c.customerName HAVING count > 2;

To join two tables from different sources

In the following example, Customer_S3 is a Hive table that loads a CSV file stored in Amazon S3 and hive_purchases is a table that references data in DynamoDB. The following example joins together customer data stored as a CSV file in Amazon S3 with order data stored in DynamoDB to return a set of data that represents orders placed by customers who have "Miller" in their name.

CREATE EXTERNAL TABLE hive_purchases(customerId bigint, total_cost double, items_purchased array) STORED BY 'org.apache.hadoop.hive.dynamodb.DynamoDBStorageHandler' TBLPROPERTIES ("dynamodb.table.name" = "Purchases", "dynamodb.column.mapping" = "customerId:CustomerId,total_cost:Cost,items_purchased:Items");

CREATE EXTERNAL TABLE Customer_S3(customerId bigint, customerName string, customerAddress array<String>)
ROW FORMAT DELIMITED FIELDS TERMINATED BY ',' 
LOCATION 's3://bucketname/path/subpath/';

Select c.customerId, c.customerName, c.customerAddress from 
Customer_S3 c 
JOIN hive_purchases p 
ON c.customerid=p.customerid 
where c.customerName like '%Miller%';

for more information you can read the documentation DynamoDB Export , Import Querys

good luck and try

Answer 2

好吧，将sql迁移到NoSQL是一个很难的决定，你可能想看一下这个白页 ，看看你的应用程序是否可以在NoSQL世界中生存。

Answer 3

Are you after this for data migration purposes? Or for your app?

Do you have an example of the data you're trying to join? Data modelling differs dramatically between SQL and NoSQL databases so as @AndrewTempleton said, you may need to denormalize your data. One of the keys to modelling with DynamoDB is understanding the access patterns for your data. Couple this with the logical structure of your data and you can begin to model it effectively.

If it's for your app, you may be able to create a single table and nest your joined table inside your parent table - so no need to join anything.

If you continue to have two tables, there's no referential integrity, unless you build it yourself. If you want to join the two tables, you need to do that programmatically - an outer loop of GetItem calls (or BatchGetItem) for your parent and an inner loop of GetItem calls for your child.

Alternatively, you can keep the two tables and use DynamoDB streams and build a denormalized "view" of the two tables. Some considerations around consistency need to the thought about.

So, in essence, a join in DynamoDB is just a couple of loops. It's very different thinking.

If you want to continue in the RDBMS world, have you considered RDS for MySQL.