Nulls Example

This page provides examples of using nulls in stream workers.

Input

Below event is sent to ProductInputStream,

['Cake', 12.0]

Output

After processing, the following events will be arriving at each stream:

• ProductValidationStream: [Cake, false]
• DiscountValidationStream: [Cake, 12.0, null, true, true, false, true, false]

Example

CREATE STREAM ProductInputStream (item string, price double);

-- Empty `ProductInfoTable` with attributes `item` and `discount`.
CREATE TABLE GLOBAL ProductInfoTable (item string, discount double);

@info(name = 'Check-for-null')
-- Checks if `price` contains `null` value.
insert into ProductValidationStream
select item, price is null as isPriceNull
-- Filter events with `item` not having `null` value.
from ProductInputStream [not(item is null)];

@info(name = 'Outer-join-with-table')
insert into DiscountValidationStream
select s.item, s.price, t.discount,
-- Check if `math:power()` returns `null`.
       math:power(t.discount, 2) is null
            as isFunctionReturnsNull,
-- Check if streams `t` and `s` are `null`.
       t is null as isTNull,
       s is null as isSNull,
-- Check if streams attributes `t.discount` and `s.item` are `null`.
       t.discount is null as isTDiscountNull,
       s.item is null as isSItemNull
from ProductInputStream as s
    left outer join ProductInfoTable as t
    on s.item == t.item;