Use the CREATE STATISTICS statement to generate table statistics for the cost-based optimizer to use.

Once you create a table and load data into it (e.g., INSERT, IMPORT), table statistics can be generated. Table statistics help the cost-based optimizer determine the cardinality of the rows used in each query, which helps to predict more accurate costs.

CREATE STATISTICS automatically figures out which columns to get statistics on — specifically, it chooses:

  • Columns that are part of the primary key or an index (in other words, all indexed columns).
  • Up to 100 non-indexed columns (unless you specify which columns to create statistics on, as shown in this example).
Note:

Automatic statistics is enabled by default; most users don't need to issue CREATE STATISTICS statements directly.

Synopsis

CREATE STATISTICS statistics_name opt_stats_columns FROM create_stats_target opt_as_of_clause

Required Privileges

The user must have the CREATE privilege on the parent database.

Parameters

Parameter Description
statistics_name The name of the set of statistics you are creating.
opt_stats_columns The name of the column(s) you want to create statistics for.
create_stats_target The name of the table you want to create statistics for.
opt_as_of_clause Used to create historical stats using the AS OF SYSTEM TIME clause. For instructions, see Create statistics as of a given time.

Examples

Create statistics on a specific column

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> CREATE STATISTICS students ON id FROM students_by_list;
Note:

Multi-column statistics are not supported yet.

Create statistics on a default set of columns

The CREATE STATISTICS statement shown below automatically figures out which columns to get statistics on — specifically, it chooses:

  • Columns that are part of the primary key or an index (in other words, all indexed columns).
  • Up to 100 non-indexed columns.
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> CREATE STATISTICS students FROM students_by_list;

Create statistics as of a given time

To create statistics as of a given time (in this example, 1 minute ago to avoid interfering with the production workload), run a statement like the following:

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> CREATE STATISTICS employee_stats FROM employees AS OF SYSTEM TIME '-1m';

For more information about how the AS OF SYSTEM TIME clause works, including supported time formats, see AS OF SYSTEM TIME.

Delete statistics

To delete statistics for all tables in all databases:

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> DELETE FROM system.table_statistics WHERE true;

To delete a named set of statistics (e.g, one named "my_stats"), run a query like the following:

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> DELETE FROM system.table_statistics WHERE name = 'my_stats';

After deleting statistics, restart the nodes in your cluster to clear the statistics caches.

For more information about the DELETE statement, see DELETE.

View statistics jobs

Every time the CREATE STATISTICS statement is executed, it kicks off a background job. This is true for queries issued by your application as well as queries issued by the automatic stats feature.

To view statistics jobs, there are two options:

  1. Use SHOW JOBS to see all statistics jobs that were created by user queries (i.e., someone entering CREATE STATISTICS at the SQL prompt or via application code):

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    > SELECT * FROM [SHOW JOBS] WHERE job_type LIKE '%CREATE STATS%';
    
           job_id       |   job_type   |                           description                            | statement | user_name |  status   | running_status |          created           |          started           |          finished          |          modified          | fraction_completed | error | coordinator_id 
    --------------------+--------------+------------------------------------------------------------------+-----------+-----------+-----------+----------------+----------------------------+----------------------------+----------------------------+----------------------------+--------------------+-------+----------------
     441281249412743169 | CREATE STATS | CREATE STATISTICS salary_stats FROM employees.public.salaries    |           | root      | succeeded |                | 2019-04-08 15:52:30.040531 | 2019-04-08 15:52:30.046646 | 2019-04-08 15:52:32.757519 | 2019-04-08 15:52:32.757519 |                  1 |       |              1
     441281163978637313 | CREATE STATS | CREATE STATISTICS employee_stats FROM employees.public.employees |           | root      | succeeded |                | 2019-04-08 15:52:03.968099 | 2019-04-08 15:52:03.972557 | 2019-04-08 15:52:05.168809 | 2019-04-08 15:52:05.168809 |                  1 |       |              1
    (2 rows)
    
  2. Use SHOW AUTOMATIC JOBS to see statistics jobs that were created by the automatic statistics feature:

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    > SELECT * FROM [SHOW AUTOMATIC JOBS] WHERE job_type LIKE '%CREATE STATS%';
    
           job_id       |     job_type      |                        description                         |                                         statement                                         | user_name |  status   | running_status |          created           |          started           |          finished          |          modified          | fraction_completed | error | coordinator_id 
    --------------------+-------------------+------------------------------------------------------------+-------------------------------------------------------------------------------------------+-----------+-----------+----------------+----------------------------+----------------------------+----------------------------+----------------------------+--------------------+-------+----------------
     441280366254850049 | AUTO CREATE STATS | Table statistics refresh for employees.public.departments  | CREATE STATISTICS __auto__ FROM [55] WITH OPTIONS THROTTLING 0.9 AS OF SYSTEM TIME '-30s' | root      | succeeded |                | 2019-04-08 15:48:00.522119 | 2019-04-08 15:48:00.52663  | 2019-04-08 15:48:00.541608 | 2019-04-08 15:48:00.541608 |                  1 |       |              1
     441280364809289729 | AUTO CREATE STATS | Table statistics refresh for employees.public.titles       | CREATE STATISTICS __auto__ FROM [60] WITH OPTIONS THROTTLING 0.9 AS OF SYSTEM TIME '-30s' | root      | succeeded |                | 2019-04-08 15:48:00.080971 | 2019-04-08 15:48:00.083117 | 2019-04-08 15:48:00.515766 | 2019-04-08 15:48:00.515767 |                  1 |       |              1
     441280356286201857 | AUTO CREATE STATS | Table statistics refresh for employees.public.salaries     | CREATE STATISTICS __auto__ FROM [59] WITH OPTIONS THROTTLING 0.9 AS OF SYSTEM TIME '-30s' | root      | succeeded |                | 2019-04-08 15:47:57.479929 | 2019-04-08 15:47:57.482235 | 2019-04-08 15:48:00.075025 | 2019-04-08 15:48:00.075025 |                  1 |       |              1
     441280352161693697 | AUTO CREATE STATS | Table statistics refresh for employees.public.employees    | CREATE STATISTICS __auto__ FROM [58] WITH OPTIONS THROTTLING 0.9 AS OF SYSTEM TIME '-30s' | root      | succeeded |                | 2019-04-08 15:47:56.221223 | 2019-04-08 15:47:56.223664 | 2019-04-08 15:47:57.474159 | 2019-04-08 15:47:57.474159 |                  1 |       |              1
     441280352070434817 | AUTO CREATE STATS | Table statistics refresh for employees.public.dept_manager | CREATE STATISTICS __auto__ FROM [57] WITH OPTIONS THROTTLING 0.9 AS OF SYSTEM TIME '-30s' | root      | succeeded |                | 2019-04-08 15:47:56.193375 | 2019-04-08 15:47:56.195813 | 2019-04-08 15:47:56.215114 | 2019-04-08 15:47:56.215114 |                  1 |       |              1
     441280350791401473 | AUTO CREATE STATS | Table statistics refresh for employees.public.dept_emp     | CREATE STATISTICS __auto__ FROM [56] WITH OPTIONS THROTTLING 0.9 AS OF SYSTEM TIME '-30s' | root      | succeeded |                | 2019-04-08 15:47:55.803052 | 2019-04-08 15:47:55.806071 | 2019-04-08 15:47:56.187153 | 2019-04-08 15:47:56.187154 |                  1 |       |              1
     441279760786096129 | AUTO CREATE STATS | Table statistics refresh for test.public.kv                | CREATE STATISTICS __auto__ FROM [53] WITH OPTIONS THROTTLING 0.9 AS OF SYSTEM TIME '-30s' | root      | succeeded |                | 2019-04-08 15:44:55.747725 | 2019-04-08 15:44:55.754582 | 2019-04-08 15:44:55.775664 | 2019-04-08 15:44:55.775665 |                  1 |       |              1
    (7 rows)
    

See Also



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