Microsoft SQL Server 2008 R2 Specifications download pdf (Page 181)

Application Development CHAPTER 8 161

Joins

You can use a join operation to match events from two streams. The CEP server rst matches

events only if they have overlapping time intervals, and then applies the conditions that you

specify in the join predicate. The output of a join operation is a new event that combines pay-

loads from the two matched events. Here is the code to join events from two input streams,

where eld x is the same value in each event. This code creates a new event containing elds

x and y from the rst event and eld y from the second event.

var outputStream = from e1 in inputStream1

join e2 in inputStream2

on e1.x equals e2.x

select new { e1.x, e1.y, e2.y };

Another option is to use a cross join, which combines all events in the rst input stream

with all events in the second input stream. You specify a cross join by using a from clause for

each input stream and then creating a new event that includes elds from the events in each

stream. By adding a where clause, you can lter the events in each stream before the CEP

server performs the cross join. The following example selects events with a value for eld x

greater than 5 from the rst stream and selects events with a value for eld y less than 20

from the second stream, performs the cross join, and then creates a stream of new events

containing eld x from the rst event and eld y from the second event:

var outputStream = from e1 in inputStream1

from e2 in inputStream2

where e1.x > 5 && e2.y < 20

select new { e1.x, e2.y };

Unions

You can also combine events from multiple streams by performing a union operation. You

can work with only two streams at a time, but you can cascade a series of union operations if

you need to combine events from three or more streams, as shown in the following code:

var outputStreamTemp = inputStream1.Union(inputStream2);

var outputStream = outputStreamTemp.Union(inputStream3);

User-dened Functions

When you need to perform an operation that the CEP server does not natively support, you

can create user-dened functions (UDFs) by reusing existing .NET functions. You add a UDF to

the CEP server in the same way that you add an adapter. You can then call the UDF anywhere

in your query where an expression can be used, such as in a lter predicate, a join predicate,

or a projection.

1 2 ... 176 177 178 179 180 181 182 183 184 185 186 ... 235 236

No comments

Microsoft SQL Server 2008 R2 Specifications Page 181