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UNION (Azure Stream Analytics)

  • مقالة

Combines the results of two or more queries into a single result set that includes all the rows that belong to all queries in the union. The UNION operation is different from using joins that combine columns from two tables.

The following are basic rules for combining the result sets of two queries by using UNION:

  • Streams must have the same partition key and partition count (learn more about partitions here)
  • The number and the order of the columns must be the same in all queries.
  • The data types must be compatible.

Important

If the inputs have a different number of partitions, scaling is not possible as scaling a Stream Analytics job takes advantage of partitions in the input and output.

Syntax

  { <query_specification> | ( <query_expression> ) }   
  UNION  
  <query_specification | ( <query_expression> )   
 [ UNION <query_specification> | ( <query_expression> )   
    [ ...n ] ]

Arguments

<query_specification> | ( <query_expression> )

Is a query specification or query expression that returns data to be combined with the data from another query specification or query expression. The definitions of the columns that are part of a UNION operation have to be the same or must be named same using an alias and must be compatible.

UNION

Specifies that multiple result sets are to be combined and returned as a single result set. UNION incorporates all rows into the results. This includes duplicates.

Example

SELECT TollId, EntryTime AS Time, LicensePlate   
FROM Input1 TIMESTAMP BY EntryTime   
UNION  
SELECT TollId, ExitTime AS Time, LicensePlate   
FROM Input2 TIMESTAMP BY ExitTime

If need be, streams can be repartitioned to match (either in the same job as below, or another one to achieve better performance):

WITH Input1_P as (
SELECT * FROM Input1 PARTITION BY partitionId INTO 2
),

Input2_P as (
SELET * FROM Input2 PARTITION BY partitionId INTO 2
)

SELECT TollId, EntryTime AS Time, LicensePlate   
FROM Input1_P TIMESTAMP BY EntryTime
UNION  
SELECT TollId, ExitTime AS Time, LicensePlate   
FROM Input2_P TIMESTAMP BY ExitTime