Database Reference
In-Depth Information
been created when the data was originally exported or simply could have
been created over existing HDFS data. Either way, you simply reference the
external table just like you would any other table. Following is a simple
example:
CREATE TABLE dbo.FactInternetSales_Import
WITH (DISTRIBUTION = HASH([SalesOrderNumber]))
AS SELECT *
FROM HDFS_FactInternetSales fis
JOIN DimCustomer cus ON fis.CustomerKey =
cus.CustomerKey
;
To facilitate the move from HDFS, the DMS has introduced a new
movement type: the
ExternalShuffleOperation
. This movement
selects the data “through” the external table (which provides PDW with the
metadata required to access the data from HDFS) and shuffles the data
using the DMS hashing function, distributing the data according to the hash
(see
Figure 10.12
); first loading the data into a temp table, known as a Q
table and then Inserting that data into the target user table.
