Databases Reference
In-Depth Information
•
Rows: 121317
. This is the number of rows that existed in the table when the statistics
object was created or last updated.
•
Rows Sampled: 111078
. This is the number of rows sampled when the statistics
object was created or last updated.
•
Steps: 200
. This is the number of steps of the histogram, which will be explained in
the next major section.
•
Density: 0.07004219
. This density value is no longer used by the Query Optimizer
and it is only included for backward compatibility.
•
Average
key
length:
8
. This is the average number of bytes for the columns of the
statistics object.
•
String Index. NO
. This value indicates if the statistics object contains string
statistics and the only choices are
YES
or
NO
; SQL Server does not provide additional
details about the string statistics. String statistics contain the data distribution for
string columns, and can help to estimate the cardinality of queries with
LIKE
conditions. As indicated before, string statistics are only created for the first column,
and only when the column is of a string data type.
•
Filter
Expression
and
Unfiltered
Rows
. These columns will be explained in the
filtered statistics section, later in the chapter.
Below the header you'll find the density vector, which includes a wealth of potentially
useful density information and will be explained in the next section.
Density
To better explain the density vector, run the statement in Listing 3-6 to inspect the
statistics of the existing index,
IX_SalesOrderDetail_ProductID
.
