PG_STATS
PG_STATS provides access to the single-column statistics stored in the pg_statistic table.
Table 1 PG_STATS columns
Name | Type | Reference | Description |
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schemaname | name | PG_NAMESPACE.nspname | Name of the schema that contains a table |
tablename | name | PG_CLASS.relname | Table name |
attname | name | PG_ATTRIBUTE.attname | Field name |
inherited | Boolean | - | Includes inherited sub-columns if the value is true; otherwise, it indicates the column in a specified table. |
null_frac | real | - | Percentage of column entries that are null |
avg_width | integer | - | Average width in bytes of column's entries |
n_distinct | real | - | - Estimated number of distinct values in the column if the value is greater than 0
- Negative of the number of distinct values divided by the number of rows if the value is less than 0
- The negated form is used when ANALYZE believes that the number of distinct values is likely to increase as the table grows.
- The positive form is used when the column seems to have a fixed number of possible values. For example, -1 indicates that the number of distinct values is the same as the number of rows for a unique column.
|
n_dndistinct | real | - | Number of unique non-null data values in the dn1 column - Exact number of distinct values if the value is greater than 0.
- Negative of the number of distinct values divided by the number of rows if the value is less than 0 For example, if the value of a column appears twice in average, set n_dndistinct=-0.5.
- The number of distinct values is unknown if the value is 0.
|
most_common_vals | anyarray | - | List of the most common values in a column. (NULL if no values in the column seem to be more common than any others) |
most_common_freqs | real[] | - | List of the frequencies of the most common values, that is, number of occurrences of each divided by total number of rows. (NULL if most_common_vals is NULL) |
histogram_bounds | anyarray | - | List of values that divide the column's values into groups of equal proportion. The values in most_common_vals, if present, are omitted from this histogram calculation. This field is null if the field data type does not have a < operator or if the most_common_vals list accounts for the entire population. |
correlation | real | - | Statistical correlation between physical row ordering and logical ordering of the column values. It ranges from -1 to +1. When the value is near to -1 or +1, an index scan on the column is estimated to be cheaper than when it is near to zero, due to reduction of random access to the disk. This column is null if the column data type does not have a < operator. |
most_common_elems | anyarray | - | A list of non-null element values most often appearing |
most_common_elem_freqs | real[] | - | A list of the frequencies of the most common element values |
elem_count_histogram | real[] | - | A histogram of the counts of distinct non-null element values |
openGauss 2024-05-06 00:44:54