System Tables
Most system tables store their data in RAM. A DatabendQuery server creates such system tables at the start.
system.numbers
This table contains a single UInt64 column named number that contains almost all the natural numbers starting from zero.
You can use this table for tests, or if you need to do a brute force search.
Reads from this table are parallelized too.
Used for tests.
mysql> SELECT avg(number) FROM numbers(100000000);
+-------------+
| avg(number) |
+-------------+
| 49999999.5 |
+-------------+
1 row in set (0.04 sec)
system.numbers_mt
The same as system.numbers
system.settings
Contains information about session settings for current user.
mysql> SELECT * FROM system.settings;
+----------------+---------+---------------------------------------------------------------------------------------------------+
| name | value | description |
+----------------+---------+---------------------------------------------------------------------------------------------------+
| max_block_size | 10000 | Maximum block size for reading |
| max_threads | 8 | The maximum number of threads to execute the request. By default, it is determined automatically. |
| default_db | default | The default database for current session |
+----------------+---------+---------------------------------------------------------------------------------------------------+
3 rows in set (0.00 sec)
system.functions
Contains information about normal and aggregate functions.
mysql> SELECT * FROM system.functions limit 10;
+----------+--------------+
| name | is_aggregate |
+----------+--------------+
| + | false |
| plus | false |
| - | false |
| minus | false |
| * | false |
| multiply | false |
| / | false |
| divide | false |
| % | false |
| modulo | false |
+----------+--------------+
10 rows in set (0.01 sec)
system.contributors
Contains information about contributors.
mysql> SELECT * FROM system.contributors LIMIT 20;
+-------------------------+
| name |
+-------------------------+
| artorias1024 |
| BohuTANG |
| dependabot[bot] |
| dependabot-preview[bot] |
| drdr xp |
| Eason |
| hulunbier |
| jyizheng |
| leiysky |
| smallfish |
| sundy-li |
| sundyli |
| taiyang-li |
| TLightSky |
| Winter Zhang |
| wubx |
| yizheng |
| Yizheng Jiao |
| zhang2014 |
| zhihanz |
+-------------------------+
20 rows in set (0.00 sec)
system.credits
Contains information about credits.
mysql> SELECT * FROM system.credits LIMIT 20;
+-------------------+---------+---------------------------+
| name | version | license |
+-------------------+---------+---------------------------+
| addr2line | 0.16.0 | Apache-2.0 OR MIT |
| adler | 1.0.2 | 0BSD OR Apache-2.0 OR MIT |
| ahash | 0.6.3 | Apache-2.0 OR MIT |
| ahash | 0.7.4 | Apache-2.0 OR MIT |
| aho-corasick | 0.7.18 | MIT OR Unlicense |
| ansi_term | 0.9.0 | MIT |
| ansi_term | 0.11.0 | MIT |
| ansi_term | 0.12.1 | MIT |
| anyhow | 1.0.43 | Apache-2.0 OR MIT |
| arbitrary | 1.0.1 | Apache-2.0 OR MIT |
| arrayvec | 0.4.12 | Apache-2.0 OR MIT |
| arrayvec | 0.5.2 | Apache-2.0 OR MIT |
| arrow-flight | 0.1.0 | Apache-2.0 |
| arrow2 | 0.4.0 | Apache-2.0 |
| assert_cmd | 2.0.1 | Apache-2.0 OR MIT |
| async-compat | 0.2.1 | Apache-2.0 OR MIT |
| async-raft | 0.6.1 | Apache-2.0 OR MIT |
| async-stream | 0.3.2 | MIT |
| async-stream-impl | 0.3.2 | MIT |
| async-trait | 0.1.51 | Apache-2.0 OR MIT |
+-------------------+---------+---------------------------+
20 rows in set (1.33 sec)