Contains information about parts and columns of [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) tables.
Each row describes one data part.
Columns:
-`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.
Formats:
-`YYYYMM` for automatic partitioning by month.
-`any_string` when partitioning manually.
-`name` ([String](../../sql-reference/data-types/string.md)) — Name of the data part.
-`part_type` ([String](../../sql-reference/data-types/string.md)) — The data part storing format.
Possible values:
-`Wide` — Each column is stored in a separate file in a filesystem.
-`Compact` — All columns are stored in one file in a filesystem.
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.
-`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.
-`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).
-`rows` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The number of rows.
-`bytes_on_disk` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of all the data part files in bytes.
-`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.
-`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.
-`marks_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of the file with marks.
-`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.
-`remove_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — The time when the data part became inactive.
-`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.
-`min_date` ([Date](../../sql-reference/data-types/date.md)) — The minimum value of the date key in the data part.
-`max_date` ([Date](../../sql-reference/data-types/date.md)) — The maximum value of the date key in the data part.
-`partition_id` ([String](../../sql-reference/data-types/string.md)) — ID of the partition.
-`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.
-`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.
-`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.
-`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`).
-`primary_key_bytes_in_memory` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The amount of memory (in bytes) used by primary key values.
-`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.
-`database` ([String](../../sql-reference/data-types/string.md)) — Name of the database.
-`table` ([String](../../sql-reference/data-types/string.md)) — Name of the table.
-`engine` ([String](../../sql-reference/data-types/string.md)) — Name of the table engine without parameters.
-`disk_name` ([String](../../sql-reference/data-types/string.md)) — Name of a disk that stores the data part.
-`path` ([String](../../sql-reference/data-types/string.md)) — Absolute path to the folder with data part files.
-`column` ([String](../../sql-reference/data-types/string.md)) — Name of the column.
-`column_position` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Ordinal position of a column in a table starting with 1.
-`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.
-`default_expression` ([String](../../sql-reference/data-types/string.md)) — Expression for the default value, or an empty string if it is not defined.
-`column_bytes_on_disk` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of the column in bytes.
-`column_data_compressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of compressed data in the column, in bytes.
-`column_data_uncompressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of the decompressed data in the column, in bytes.
-`column_marks_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of the column with marks, in bytes.
-`bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Alias for `bytes_on_disk`.
-`marks_size` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Alias for `marks_bytes`.
**Example**
``` sql
SELECT * FROM system.parts_columns LIMIT 1 FORMAT Vertical;
