Query statistics

After statistics are collected or when you want to confirm whether statistics exist for a table, OceanBase Database provides various views to query statistics.

Query index and table-level statistics

To query table-level and index statistics, you can query the following views.

The following fields are important in the views:

• NUM_ROWS: the total number of rows in a table or index.
• AVG_ROW_LEN: the average row length of a table.
• LAST_ANALYZED: the time when statistics are collected. If this field is not NULL, statistics are collected for the table or index.
• STATTYPE_LOCKED: specifies whether statistics of a table are locked. If this field is not NULL, statistics of the table are locked.

Query column-level statistics

To query column-level statistics, you can query the following views.

The following fields are important in the views:

• NUM_DISTINCT: the number of distinct values (NDV) of a column.
• LOW_VALUE: the minimum value of a column.
• HIGH_VALUE: the maximum value of a column.
• DENSITY: the density of a column, which is related to histograms.
• NUM_NULLS: the number of NULL values in a column.
• NUM_BUCKETS: the number of histogram buckets.
• LAST_ANALYZED: the time when statistics are collected. If this field is not NULL, statistics are collected for the column at some point in the past.
• SAMPLE_SIZE: the number of data rows used to collect statistics.
• AVG_COL_LEN: the average column length.
• HISTOGRAM: the histogram type. If this field is not NULL, a histogram is collected for the column.

Query column histogram statistics

To query histogram statistics, you can query the following views.

The following fields are important in the views:

• ENDPOINT_NUMBER: the total number of rows in the column up to the current bucket.
• ENDPOINT_ACTUAL_VALUE: the printed character value corresponding to the end value of the current bucket.
• ENDPOINT_REPEAT_COUNT: the frequency of the end value of the current bucket.