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Null

Provides examples on using nulls in Siddhi Apps.

For more information refer Siddhi query guide.

define stream ProductInputStream (item string, price double);

define Table ProductInfoTable (item string, discount double);

@info(name = 'Check-for-null')
from ProductInputStream [not(item is null)]
select item,
       price is null as isPriceNull
insert into ProductValidationStream;

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

define stream ProductInputStream (item string, price double);
define Table ProductInfoTable (item string, discount double);	Empty ProductInfoTable with attributes item and discount.
@info(name = 'Check-for-null')
from ProductInputStream [not(item is null)]	Filter events with item not having null value.
select item,
price is null as isPriceNull	Checks if price contains null value.
insert into ProductValidationStream;
@info(name = 'Outer-join-with-table') from ProductInputStream as s left outer join ProductInfoTable as t on s.item == t.item select s.item, s.price, t.discount,
math:power(t.discount, 2) is null as isFunctionReturnsNull,	Check if math:power() returns null.
t is null as isTNull, s is null as isSNull,	Check if streams t and s are null.
t.discount is null as isTDiscountNull, s.item is null as isSItemNull	Check if streams attributes t.discount and s.item are null.
insert into DiscountValidationStream;

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]

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