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7.9 KiB
Markdown
150 lines
7.9 KiB
Markdown
---
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slug: /en/operations/system-tables/parts_columns
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---
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# parts_columns
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Contains information about parts and columns of [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) tables.
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Each row describes one data part.
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Columns:
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- `partition` ([String](../../sql-reference/data-types/string.md)) — The partition name. To learn what a partition is, see the description of the [ALTER](../../sql-reference/statements/alter/index.md#query_language_queries_alter) query.
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Formats:
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- `YYYYMM` for automatic partitioning by month.
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- `any_string` when partitioning manually.
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- `name` ([String](../../sql-reference/data-types/string.md)) — Name of the data part.
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- `part_type` ([String](../../sql-reference/data-types/string.md)) — The data part storing format.
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Possible values:
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- `Wide` — Each column is stored in a separate file in a filesystem.
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- `Compact` — All columns are stored in one file in a filesystem.
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Data storing format is controlled by the `min_bytes_for_wide_part` and `min_rows_for_wide_part` settings of the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) table.
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- `active` ([UInt8](../../sql-reference/data-types/int-uint.md)) — Flag that indicates whether the data part is active. If a data part is active, it’s used in a table. Otherwise, it’s deleted. Inactive data parts remain after merging.
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- `marks` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The number of marks. To get the approximate number of rows in a data part, multiply `marks` by the index granularity (usually 8192) (this hint does not work for adaptive granularity).
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- `rows` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The number of rows.
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- `bytes_on_disk` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of all the data part files in bytes.
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- `data_compressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of compressed data in the data part. All the auxiliary files (for example, files with marks) are not included.
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- `data_uncompressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of uncompressed data in the data part. All the auxiliary files (for example, files with marks) are not included.
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- `marks_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of the file with marks.
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- `modification_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — The time the directory with the data part was modified. This usually corresponds to the time of data part creation.
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- `remove_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — The time when the data part became inactive.
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- `refcount` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The number of places where the data part is used. A value greater than 2 indicates that the data part is used in queries or merges.
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- `min_date` ([Date](../../sql-reference/data-types/date.md)) — The minimum value of the date key in the data part.
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- `max_date` ([Date](../../sql-reference/data-types/date.md)) — The maximum value of the date key in the data part.
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- `partition_id` ([String](../../sql-reference/data-types/string.md)) — ID of the partition.
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- `min_block_number` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The minimum number of data parts that make up the current part after merging.
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- `max_block_number` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The maximum number of data parts that make up the current part after merging.
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- `level` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Depth of the merge tree. Zero means that the current part was created by insert rather than by merging other parts.
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- `data_version` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Number that is used to determine which mutations should be applied to the data part (mutations with a version higher than `data_version`).
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- `primary_key_bytes_in_memory` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The amount of memory (in bytes) used by primary key values.
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- `primary_key_bytes_in_memory_allocated` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The amount of memory (in bytes) reserved for primary key values.
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- `database` ([String](../../sql-reference/data-types/string.md)) — Name of the database.
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- `table` ([String](../../sql-reference/data-types/string.md)) — Name of the table.
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- `engine` ([String](../../sql-reference/data-types/string.md)) — Name of the table engine without parameters.
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- `disk_name` ([String](../../sql-reference/data-types/string.md)) — Name of a disk that stores the data part.
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- `path` ([String](../../sql-reference/data-types/string.md)) — Absolute path to the folder with data part files.
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- `column` ([String](../../sql-reference/data-types/string.md)) — Name of the column.
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- `type` ([String](../../sql-reference/data-types/string.md)) — Column type.
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- `column_position` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Ordinal position of a column in a table starting with 1.
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- `default_kind` ([String](../../sql-reference/data-types/string.md)) — Expression type (`DEFAULT`, `MATERIALIZED`, `ALIAS`) for the default value, or an empty string if it is not defined.
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- `default_expression` ([String](../../sql-reference/data-types/string.md)) — Expression for the default value, or an empty string if it is not defined.
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- `column_bytes_on_disk` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of the column in bytes.
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- `column_data_compressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of compressed data in the column, in bytes.
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- `column_data_uncompressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of the decompressed data in the column, in bytes.
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- `column_marks_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of the column with marks, in bytes.
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- `bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Alias for `bytes_on_disk`.
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- `marks_size` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Alias for `marks_bytes`.
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**Example**
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``` sql
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SELECT * FROM system.parts_columns LIMIT 1 FORMAT Vertical;
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```
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``` text
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Row 1:
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──────
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partition: tuple()
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name: all_1_2_1
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part_type: Wide
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active: 1
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marks: 2
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rows: 2
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bytes_on_disk: 155
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data_compressed_bytes: 56
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data_uncompressed_bytes: 4
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marks_bytes: 96
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modification_time: 2020-09-23 10:13:36
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remove_time: 2106-02-07 06:28:15
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refcount: 1
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min_date: 1970-01-01
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max_date: 1970-01-01
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partition_id: all
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min_block_number: 1
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max_block_number: 2
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level: 1
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data_version: 1
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primary_key_bytes_in_memory: 2
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primary_key_bytes_in_memory_allocated: 64
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database: default
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table: 53r93yleapyears
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engine: MergeTree
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disk_name: default
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path: /var/lib/clickhouse/data/default/53r93yleapyears/all_1_2_1/
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column: id
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type: Int8
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column_position: 1
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default_kind:
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default_expression:
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column_bytes_on_disk: 76
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column_data_compressed_bytes: 28
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column_data_uncompressed_bytes: 2
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column_marks_bytes: 48
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```
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**See Also**
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- [MergeTree family](../../engines/table-engines/mergetree-family/mergetree.md)
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