• Article

Statistics Properties (Details Page)

The Details page of the Statistics Properties dialog box shows the information collected in the currently selected statistic object. This information is used by the query optimizer to create the best possible query plan.

Statistics can be collected by examining every row in the table or by sampling a large table. When sampling was used, or when statistics are out of date, the statistics presented in the page may not reflect the exact state of the table. The statistics displayed are read-only.

Options

  • Table Name
    Displays the name of the table described by the statistics.

  • Statistics Name
    Displays the name of the database object where the statistics are stored. Statistics unrelated to an index which were created automatically by Microsoft SQL Server have names beginning with _WA_Sys.

  • Statistics for
    Displays the name of the statistics object.

  • Updated
    Displays the date the current statistics were created.

  • Rows
    Displays the number of rows in the table.

  • Rows Sampled
    Displays the number of rows examined to create the statistics.

  • Steps
    The rows of the table are split into groups for the statistics histogram. This is the number of groups that were created.

  • Density
    An index that has a large number of duplicates has high density.

    A unique index has low density.

  • Average Key Length
    Displays the average length of each row.

  • String Index
    Yes indicates that the statistics contain a string summary index to support estimation of result set sizes for LIKE conditions. (Applies only to leading columns of char, varchar, nchar, and nvarchar data types.)

Data for Columns

  • All Density
    Displays the density for the combination of columns listed in the Columns section.

  • Average Length
    Displays the average length of the combination of columns listed in the Columns section.

  • Columns
    Displays the columns described by the All Density and the Average Length fields.

The Histogram Steps

  • RANGE_HI_KEY
    Displays the upper bound value of a histogram step.

  • RANGE_ROWS
    Displays the number of rows from the sample that fall within a histogram step, excluding the upper bound.

  • EQ_ROWS
    Displays the number of rows from the sample that are equal in value to the upper bound of the histogram step.

  • DISTINCT_RANGE_ROWS
    Displays the number of distinct values within a histogram step, excluding the upper bound.

  • AVG_RANGE_ROWS
    Displays the average number of duplicate values within a histogram step, excluding the upper bound value (RANGE_ROWS / DISTINCT_RANGE_ROWS for DISTINCT_RANGE_ROWS > 0).