Updated on 2024-06-03 GMT+08:00

DB_TAB_COL_STATISTICS

DB_TAB_COL_STATISTICS displays column statistics and histogram information extracted from DB_TAB_COLUMNS. All users can access this view. This view exists in both PG_CATALOG and SYS schema. The values of the LOW_VALUE and HIGH_VALUE columns in this view are different from those in database A due to different underlying table structures. When the value of LOW_VALUE is a high-frequency value, the value of LOW_VALUE in GaussDB is the second smallest value. When HIGH_VALUE is a high-frequency value, HIGH_VALUE of GaussDB is the second highest value. The value of the HISTOGRAM column is different from that of database A due to different statistical methods. GaussDB supports only two types of histograms: frequency and equi-width. The value of the SCOPE column in GaussDB is different from that in database A because GaussDB does not support global temporary table statistics. GaussDB database supports only local temporary table statistics, and the default value is SHARED.

Table 1 DB_TAB_COL_STATISTICS columns

Name

Type

Description

owner

character varying(128)

Table owner.

table_name

character varying(128)

Table name.

column_name

character varying(128)

Column name.

num_distinct

numeric

Number of different values in a column.

low_value

raw

Low value in a column.

high_value

raw

High value in a column.

density

numeric

  • If there is a histogram on COLUMN_NAME, this column displays the selectivity of values in the histogram that span less than two endpoints. It does not represent the selectivity of values that span two or more endpoints.
  • If no histogram is available on COLUMN_NAME, the value of this column is 1/NUM_DISTINCT.

num_nulls

numeric

Number of empty values in a column.

num_buckets

numeric

Number of buckets in the histogram of a column.

sample_size

numeric

Sample size used to analyze a column.

last_analyzed

timestamp(0) without time zone

Date when a column was last analyzed. After the database is restarted, data loss will occur.

global_stats

character varying(3)

Not supported. Its value is NULL.

user_stats

character varying(3)

Not supported. Its value is NULL.

notes

character varying(99)

Not supported. Its value is NULL.

avg_col_len

numeric

Average length of a column, in bytes.

histogram

character varying(15)

Specifies whether the histogram exists and the type of the histogram.
  • NONE: no histogram.
  • FREQUENCY: frequency histogram.
  • EQUI-WIDTH: equal-width histogram.

scope

character varying(7)

For statistics collected on any table other than global temporary tables, the value is SHARED (indicating that the statistics are shared among all sessions).

schema

character varying(64)

Name of the namespace to which the column belongs.