ScalarAggOp operator

The ScalarAggOp operator keeps track of running information about an input data stream, such as the number of rows in the stream, or the maximum value of a given column in the stream.

The ScalarAggOp operator prints a list of up to 10 messages describing the scalar aggregation operations it executes. The message has the following format:

Evaluate Ungrouped  <Type of Aggregate> Aggregate

<Type of Aggregate> can be any of the following: count, sum, average, min, max, any, once-unique, count-unique, sum-unique, average-unique, or once.

The following query performs a ScalarAggOp (in other words, unwrapped) aggregation on the authors table in the pubs2 database:

1> use pubs2
2> go
1> set showplan on
2> go
1> select count(*) from authors
2> go

QUERY PLAN FOR STATEMENT 1 (at line 1).

2 operator(s) under root

The type of query is SELECT.

ROOT:EMIT Operator

	|SCALAR AGGREGATE Operator
	|  Evaluate Ungrouped COUNT AGGREGATE.
	|
	|   |SCAN Operator
	|   |  FROM TABLE
	|   |  authors
	|   |  Index : aunmind
	|   |  Forward Scan.
	|   |  Positioning at index start.
	|   |  Index contains all needed columns. Base table will not be read.
	|   |  Using I/O Size 4 Kbytes for index leaf pages.
	|   |  With LRU Buffer Replacement Strategy for index leaf pages.


----------- 
	23 

(1 row affected)

The ScalarAggOp message indicates that the query to be executed is an ungrouped count aggregation.