Views

The standard SQL view syntax (with some limitations) is now supported by Phoenix to enable multiple virtual tables to all share the same underlying physical HBase table. This is especially important in HBase, as you cannot realistically expect to have more than a hundred physical tables and get reasonable performance from HBase.

For example, given the following table definition that defines a base table to collect product metrics:

CREATE  TABLE product_metrics (
    metric_type CHAR(1),
    created_by VARCHAR, 
    created_date DATE, 
    metric_id INTEGER
    CONSTRAINT pk PRIMARY KEY (metric_type, created_by, created_date, metric_id));

You may define the following view:

CREATE VIEW mobile_product_metrics (carrier VARCHAR, dropped_calls BIGINT) AS
SELECT * FROM product_metrics
WHERE metric_type = 'm';

Notice that unlike with standard SQL views, you may define additional columns for your view. The view inherits all of the columns from its base table, in addition to being able to optionally add new KeyValue columns. You may also add these columns after-the-fact with an ALTER TABLE statement.

If your view uses only simple equality expressions in the WHERE clause, you are also allowed to issue DML against the view. These views are termed updatable views. For example, in this case you could issue the following UPSERT statement:

UPSERT INTO mobile_product_metrics(created_by, create_date, metric_id, carrier, dropped_calls)
VALUES('John Doe', CURRENT_DATE(), NEXT VALUE FOR metric_seq, 'Verizon', 20);

In this case, the metric_type column value is inferred since the VIEW defines it as 'm'.

Also, queries done through the view will automatically apply the WHERE clause filter. For example:

SELECT sum(dropped_calls) FROM mobile_product_metrics WHERE carrier='Verizon'

This would sum all the dropped_calls across all product_metrics with a metric_type of 'm' and a carrier of 'Verizon'.

Views may also be defined with more complex WHERE clauses, but in that case you cannot issue DML against them as you'll get a ReadOnlyException. You are still allowed to query through them and their WHERE clauses will be in effect as with standard SQL views.