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chore: add doc about information_schema (#2471)
* chore: add doc about information_schema * chore: add doc about information_schema
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‎docs/en/sql-reference/00-sql-reference/20-information-schema-tables/_category_.json‎

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{
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"label": "Information Schema"
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}

‎docs/en/sql-reference/00-sql-reference/20-information-schema-tables/index.md‎

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---
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title: Information_Schema Tables
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---
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## Information Schema
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| Table | Description |
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|----------------------------------------------|------------------------------------------------|
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| [tables](information-schema-tables.md) | ANSI SQL standard metadata view for tables. |
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| [schemata](information-schema-schemata.md) | ANSI SQL standard metadata view for databases. |
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| [views](information-schema-views.md) | ANSI SQL standard metadata view for views. |
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| [keywords](information-schema-keywords.md) | ANSI SQL standard metadata view for keywords. |
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| [columns](information-schema-columns.md) | ANSI SQL standard metadata view for columns. |
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```sql
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SHOW VIEWS FROM INFORMATION_SCHEMA;
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╭─────────────────────────────╮
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│ Views_in_information_schema │
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│ String │
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├─────────────────────────────┤
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│ columns │
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│ key_column_usage │
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│ keywords │
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│ schemata │
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│ statistics │
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│ tables │
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│ views │
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╰─────────────────────────────╯
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```

‎docs/en/sql-reference/00-sql-reference/20-information-schema-tables/information-schema-columns.md‎

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---
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title: information_schema.columns
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---
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Contains information about columns of tables.
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```sql
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desc information_schema.columns
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╭─────────────────────────────────────────────────────────────────────────╮
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│ Field │ Type │ Null │ Default │ Extra │
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│ String │ String │ String │ String │ String │
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├──────────────────────────┼──────────────────┼────────┼─────────┼────────┤
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│ table_catalog │ VARCHAR │ NO │ '' │ │
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│ table_schema │ VARCHAR │ NO │ '' │ │
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│ table_name │ VARCHAR │ NO │ '' │ │
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│ column_name │ VARCHAR │ NO │ '' │ │
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│ ordinal_position │ TINYINT UNSIGNED │ NO │ 0 │ │
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│ column_default │ NULL │ NO │ NULL │ │
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│ column_comment │ VARCHAR │ NO │ '' │ │
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│ column_key │ NULL │ NO │ NULL │ │
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│ nullable │ TINYINT UNSIGNED │ YES │ NULL │ │
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│ is_nullable │ VARCHAR │ NO │ '' │ │
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│ data_type │ VARCHAR │ NO │ '' │ │
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│ column_type │ VARCHAR │ NO │ '' │ │
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│ character_maximum_length │ NULL │ NO │ NULL │ │
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│ character_octet_length │ NULL │ NO │ NULL │ │
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│ numeric_precision │ NULL │ NO │ NULL │ │
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│ numeric_precision_radix │ NULL │ NO │ NULL │ │
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│ numeric_scale │ NULL │ NO │ NULL │ │
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│ datetime_precision │ NULL │ NO │ NULL │ │
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│ character_set_catalog │ NULL │ NO │ NULL │ │
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│ character_set_schema │ NULL │ NO │ NULL │ │
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│ character_set_name │ NULL │ NO │ NULL │ │
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│ collation_catalog │ NULL │ NO │ NULL │ │
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│ collation_schema │ NULL │ NO │ NULL │ │
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│ collation_name │ NULL │ NO │ NULL │ │
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│ domain_catalog │ NULL │ NO │ NULL │ │
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│ domain_schema │ NULL │ NO │ NULL │ │
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│ domain_name │ NULL │ NO │ NULL │ │
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│ privileges │ NULL │ NO │ NULL │ │
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│ default │ VARCHAR │ NO │ '' │ │
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│ extra │ NULL │ NO │ NULL │ │
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╰─────────────────────────────────────────────────────────────────────────╯
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```

‎docs/en/sql-reference/00-sql-reference/20-information-schema-tables/information-schema-keywords.md‎

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---
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title: information_schema.keywords
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---
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The `information_schema.keywords` system table is a view that provides all keywords in Databend
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```sql
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DESCRIBE information_schema.keywords
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╭─────────────────────────────────────────────────────────╮
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│ Field │ Type │ Null │ Default │ Extra │
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│ String │ String │ String │ String │ String │
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├──────────┼──────────────────┼────────┼─────────┼────────┤
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│ keywords │ VARCHAR │ NO │ '' │ │
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│ reserved │ TINYINT UNSIGNED │ NO │ 0 │ │
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╰─────────────────────────────────────────────────────────╯
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```

‎docs/en/sql-reference/00-sql-reference/20-information-schema-tables/information-schema-schemata.md‎

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---
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title: information_schema.schemata
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---
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Provides metadata about all databases in the system.
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```sql
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desc information_schema.schemata
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╭─────────────────────────────────────────────────────────────────────╮
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│ Field │ Type │ Null │ Default │ Extra │
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│ String │ String │ String │ String │ String │
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├───────────────────────────────┼─────────┼────────┼─────────┼────────┤
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│ catalog_name │ VARCHAR │ NO │ '' │ │
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│ schema_name │ VARCHAR │ NO │ '' │ │
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│ schema_owner │ VARCHAR │ NO │ '' │ │
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│ default_character_set_catalog │ NULL │ NO │ NULL │ │
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│ default_character_set_schema │ NULL │ NO │ NULL │ │
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│ default_character_set_name │ NULL │ NO │ NULL │ │
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│ default_collation_name │ NULL │ NO │ NULL │ │
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│ sql_path │ NULL │ NO │ NULL │ │
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╰─────────────────────────────────────────────────────────────────────╯
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```

‎docs/en/sql-reference/00-sql-reference/20-information-schema-tables/information-schema-tables.md‎

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---
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title: information_schema.tables
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---
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The `information_schema.tables` system table is a view that provides metadata about all tables across all databases, including their schema, type, engine, and creation details. It also includes storage metrics such as data length, index length, and row count, offering insights into table structure and usage.
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```sql
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DESCRIBE information_schema.tables;
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┌────────────────────────────────────────────────────────────────────────────────────┐
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│ Field │ Type │ Null │ Default │ Extra │
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├─────────────────┼─────────────────┼────────┼──────────────────────────────┼────────┤
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│ table_catalog │ VARCHAR │ NO │ '' │ │
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│ table_schema │ VARCHAR │ NO │ '' │ │
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│ table_name │ VARCHAR │ NO │ '' │ │
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│ table_type │ VARCHAR │ NO │ '' │ │
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│ engine │ VARCHAR │ NO │ '' │ │
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│ create_time │ TIMESTAMP │ NO │ '1970-01-01 00:00:00.000000' │ │
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│ drop_time │ TIMESTAMP │ YES │ NULL │ │
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│ data_length │ BIGINT UNSIGNED │ YES │ NULL │ │
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│ index_length │ BIGINT UNSIGNED │ YES │ NULL │ │
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│ table_rows │ BIGINT UNSIGNED │ YES │ NULL │ │
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│ auto_increment │ NULL │ NO │ NULL │ │
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│ table_collation │ NULL │ NO │ NULL │ │
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│ data_free │ NULL │ NO │ NULL │ │
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│ table_comment │ VARCHAR │ NO │ '' │ │
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└────────────────────────────────────────────────────────────────────────────────────┘
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```

‎docs/en/sql-reference/00-sql-reference/20-information-schema-tables/information-schema-views.md‎

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---
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title: information_schema.views
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---
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Provides metadata information for all views.
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See also:
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- [SHOW VIEWS](../../10-sql-commands/00-ddl/05-view/show-views.md)
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```sql
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DESCRIBE information_schema.views;
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╭───────────────────────────────────────────────────────────────────────────╮
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│ Field │ Type │ Null │ Default │ Extra │
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│ String │ String │ String │ String │ String │
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├────────────────────────────┼──────────────────┼────────┼─────────┼────────┤
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│ table_catalog │ VARCHAR │ NO │ '' │ │
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│ table_schema │ VARCHAR │ NO │ '' │ │
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│ table_name │ VARCHAR │ NO │ '' │ │
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│ view_definition │ VARCHAR │ NO │ '' │ │
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│ check_option │ VARCHAR │ NO │ '' │ │
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│ is_updatable │ TINYINT UNSIGNED │ NO │ 0 │ │
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│ is_insertable_into │ BOOLEAN │ NO │ false │ │
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│ is_trigger_updatable │ TINYINT UNSIGNED │ NO │ 0 │ │
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│ is_trigger_deletable │ TINYINT UNSIGNED │ NO │ 0 │ │
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│ is_trigger_insertable_into │ TINYINT UNSIGNED │ NO │ 0 │ │
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╰───────────────────────────────────────────────────────────────────────────╯
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```

‎docs/en/sql-reference/00-sql-reference/31-system-tables/index.md‎

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### Database & Table Metadata
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| Table | Description |
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|-------|-------------|
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| [system.tables](system-tables.md) | Provides metadata information for all tables including properties, creation time, size, and more. |
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| [system.tables_with_history](system-tables-with-history.md) | Provides historical metadata information for tables, including dropped tables. |
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| [system.databases](system-databases.md) | Contains information about all databases in the system. |
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| [system.databases_with_history](system-databases-with-history.md) | Contains historical information about databases, including dropped databases. |
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| [system.columns](system-columns.md) | Provides information about columns in all tables. |
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| [system.indexes](system-indexes.md) | Contains information about table indexes. |
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| [system.virtual_columns](system-virtual-columns.md) | Lists virtual columns available in the system. |
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| Table | Description |
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|-------------------------------------------------------------------|---------------------------------------------------------------------------------------------------|
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| [system.tables](system-tables.md) | Provides metadata information for all tables including properties, creation time, size, and more. |
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| [system.tables_with_history](system-tables-with-history.md) | Provides historical metadata information for tables, including dropped tables. |
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| [system.databases](system-databases.md) | Contains information about all databases in the system. |
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| [system.views](system-views.md) | Contains information about all views in the system. |
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| [system.databases_with_history](system-databases-with-history.md) | Contains historical information about databases, including dropped databases. |
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| [system.columns](system-columns.md) | Provides information about columns in all tables. |
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| [system.indexes](system-indexes.md) | Contains information about table indexes. |
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| [system.virtual_columns](system-virtual-columns.md) | Lists virtual columns available in the system. |
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### Query & Performance
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| [system.streams](system-streams.md) | Contains information about streams in the system. |
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| [system.temp_tables](system-temp-tables.md) | Contains information about temporary tables. |
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| [system.temp_files](system-temp-files.md) | Contains information about temporary files. |
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### Information Schema
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| Table | Description |
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|-------|-------------|
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| [information_schema.tables](information-schema-tables.md) | ANSI SQL standard metadata view for tables. |
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