CREATE VIEW

Create a new hstream view with the given name. An exception will be thrown if a view or stream with the same name already exists.

A view is NOT just an alias but physically maintained in the memory and is updated incrementally. Thus queries on a view are really fast and do not require extra resources.

Synopsis

CREATE VIEW view_name AS select_query;

Notes

• view_name is a valid identifier.
• select_query is a valid SELECT (Stream) query. For more information, see SELECT section. There is no extra restrictions on select_query but we recommend using at least one aggregate function and a GROUP BY clause. Otherwise, the query may be a little weird and consumes more resources. See the following examples:

// CREATE VIEW v1 AS SELECT id, SUM(sales) FROM s GROUP BY id EMIT CHANGES;
// what the view contains at time
//            [t1]                            [t2]                            [t3]
//  {"id":1, "SUM(sales)": 10}  ->  {"id":1, "SUM(sales)": 10}  ->  {"id":1, "SUM(sales)": 30}
//                                  {"id":2, "SUM(sales)": 8}       {"id":2, "SUM(sales)": 15}

// CREATE VIEW AS SELECT id, sales FROM s EMIT CHANGES;
// what the view contains at time
//           [t1]                       [t2]                       [t3]
// {"id":1, "sales": 10}  ->  {"id":1, "sales": 10}  ->  {"id":1, "sales": 10}
//                            {"id":2, "sales": 8}       {"id":1, "sales": 20}
//                                                       {"id":2, "sales": 8}
//                                                       {"id":2, "sales": 7}

Examples

CREATE VIEW foo AS SELECT a, SUM(a), COUNT(*) FROM s1 GROUP BY b EMIT CHANGES;
CREATE VIEW bar AS SELECT * FROM s2 EMIT CHANGES; // valid but not recommended