ClickHouse/docs/en/operations/system-tables/tables.md

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/en/operations/system-tables/tables

tables

Contains metadata of each table that the server knows about.

Detached tables are not shown in system.tables.

Temporary tables are visible in the system.tables only in those session where they have been created. They are shown with the empty database field and with the is_temporary flag switched on.

Columns:

• database (String) — The name of the database the table is in.

• name (String) — Table name.

• uuid (UUID) — Table uuid (Atomic database).

• engine (String) — Table engine name (without parameters).

• is_temporary (UInt8) - Flag that indicates whether the table is temporary.

• data_paths (Array(String)) - Paths to the table data in the file systems.

• metadata_path (String) - Path to the table metadata in the file system.

• metadata_modification_time (DateTime) - Time of latest modification of the table metadata.

• dependencies_database (Array(String)) - Database dependencies.

• dependencies_table (Array(String)) - Table dependencies (MaterializedView tables based on the current table).

• create_table_query (String) - The query that was used to create the table.

• engine_full (String) - Parameters of the table engine.

• as_select (String) - SELECT query for view.

• partition_key (String) - The partition key expression specified in the table.

• sorting_key (String) - The sorting key expression specified in the table.

• primary_key (String) - The primary key expression specified in the table.

• sampling_key (String) - The sampling key expression specified in the table.

• storage_policy (String) - The storage policy:

  • MergeTree
  • Distributed

• total_rows (Nullable(UInt64)) - Total number of rows, if it is possible to quickly determine exact number of rows in the table, otherwise NULL (including underying Buffer table).

• total_bytes (Nullable(UInt64)) - Total number of bytes, if it is possible to quickly determine exact number of bytes for the table on storage, otherwise NULL (does not includes any underlying storage).

  • If the table stores data on disk, returns used space on disk (i.e. compressed).
  • If the table stores data in memory, returns approximated number of used bytes in memory.

• lifetime_rows (Nullable(UInt64)) - Total number of rows INSERTed since server start (only for Buffer tables).

• lifetime_bytes (Nullable(UInt64)) - Total number of bytes INSERTed since server start (only for Buffer tables).

• comment (String) - The comment for the table.

• has_own_data (UInt8) — Flag that indicates whether the table itself stores some data on disk or only accesses some other source.

• loading_dependencies_database (Array(String)) - Database loading dependencies (list of objects which should be loaded before the current object).

• loading_dependencies_table (Array(String)) - Table loading dependencies (list of objects which should be loaded before the current object).

• loading_dependent_database (Array(String)) - Dependent loading database.

• loading_dependent_table (Array(String)) - Dependent loading table.

The system.tables table is used in SHOW TABLES query implementation.

Example

SELECT * FROM system.tables LIMIT 2 FORMAT Vertical;

Row 1:
──────
database:                   base
name:                       t1
uuid:                       81b1c20a-b7c6-4116-a2ce-7583fb6b6736
engine:                     MergeTree
is_temporary:               0
data_paths:                 ['/var/lib/clickhouse/store/81b/81b1c20a-b7c6-4116-a2ce-7583fb6b6736/']
metadata_path:              /var/lib/clickhouse/store/461/461cf698-fd0b-406d-8c01-5d8fd5748a91/t1.sql
metadata_modification_time: 2021-01-25 19:14:32
dependencies_database:      []
dependencies_table:         []
create_table_query:         CREATE TABLE base.t1 (`n` UInt64) ENGINE = MergeTree ORDER BY n SETTINGS index_granularity = 8192
engine_full:                MergeTree ORDER BY n SETTINGS index_granularity = 8192
as_select:                  SELECT database AS table_catalog
partition_key:
sorting_key:                n
primary_key:                n
sampling_key:
storage_policy:             default
total_rows:                 1
total_bytes:                99
lifetime_rows:              ᴺᵁᴸᴸ
lifetime_bytes:             ᴺᵁᴸᴸ
comment:
has_own_data:               0
loading_dependencies_database: []
loading_dependencies_table:    []
loading_dependent_database:    []
loading_dependent_table:       []

Row 2:
──────
database:                   default
name:                       53r93yleapyears
uuid:                       00000000-0000-0000-0000-000000000000
engine:                     MergeTree
is_temporary:               0
data_paths:                 ['/var/lib/clickhouse/data/default/53r93yleapyears/']
metadata_path:              /var/lib/clickhouse/metadata/default/53r93yleapyears.sql
metadata_modification_time: 2020-09-23 09:05:36
dependencies_database:      []
dependencies_table:         []
create_table_query:         CREATE TABLE default.`53r93yleapyears` (`id` Int8, `febdays` Int8) ENGINE = MergeTree ORDER BY id SETTINGS index_granularity = 8192
engine_full:                MergeTree ORDER BY id SETTINGS index_granularity = 8192
as_select:                  SELECT name AS catalog_name
partition_key:
sorting_key:                id
primary_key:                id
sampling_key:
storage_policy:             default
total_rows:                 2
total_bytes:                155
lifetime_rows:              ᴺᵁᴸᴸ
lifetime_bytes:             ᴺᵁᴸᴸ
comment:
has_own_data:               0
loading_dependencies_database: []
loading_dependencies_table:    []
loading_dependent_database:    []
loading_dependent_table:       []