> ## Documentation Index
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> System table containing information about parts and columns of MergeTree tables.

# system.parts_columns

<h2 id="description">
  Description
</h2>

Contains information about parts and columns of [MergeTree](/reference/engines/table-engines/mergetree-family/mergetree) tables.
Each row describes one data part.

<h2 id="columns">
  Columns
</h2>

* `partition` ([String](/reference/data-types/index)) — The partition name.
* `name` ([String](/reference/data-types/index)) — Name of the data part.
* `uuid` ([UUID](/reference/data-types/index)) — The parts UUID.
* `part_type` ([String](/reference/data-types/index)) — 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.
* `active` ([UInt8](/reference/data-types/index)) — 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](/reference/data-types/index)) — 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](/reference/data-types/index)) — The number of rows.
* `bytes_on_disk` ([UInt64](/reference/data-types/index)) — Total size of all the data part files in bytes.
* `data_compressed_bytes` ([UInt64](/reference/data-types/index)) — 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](/reference/data-types/index)) — Total size of uncompressed data in the data part. All the auxiliary files (for example, files with marks) are not included.
* `marks_bytes` ([UInt64](/reference/data-types/index)) — The size of the file with marks.
* `modification_time` ([DateTime](/reference/data-types/index)) — The time the directory with the data part was modified. This usually corresponds to the time of data part creation.
* `remove_time` ([DateTime](/reference/data-types/index)) — The time when the data part became inactive.
* `refcount` ([UInt32](/reference/data-types/index)) — 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](/reference/data-types/index)) — The minimum value for the Date column if that is included in the partition key.
* `max_date` ([Date](/reference/data-types/index)) — The maximum value for the Date column if that is included in the partition key.
* `min_time` ([DateTime](/reference/data-types/index)) — The minimum value for the DateTime column if that is included in the partition key.
* `max_time` ([DateTime](/reference/data-types/index)) — The maximum value for the DateTime column if that is included in the partition key.
* `partition_id` ([String](/reference/data-types/index)) — ID of the partition.
* `min_block_number` ([Int64](/reference/data-types/index)) — The minimum number of data parts that make up the current part after merging.
* `max_block_number` ([Int64](/reference/data-types/index)) — The maximum number of data parts that make up the current part after merging.
* `level` ([UInt32](/reference/data-types/index)) — Depth of the merge tree. Zero means that the current part was created by insert rather than by merging other parts.
* `data_version` ([UInt64](/reference/data-types/index)) — 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](/reference/data-types/index)) — The amount of memory (in bytes) used by primary key values.
* `primary_key_bytes_in_memory_allocated` ([UInt64](/reference/data-types/index)) — The amount of memory (in bytes) reserved for primary key values.
* `database` ([String](/reference/data-types/index)) — Name of the database.
* `table` ([String](/reference/data-types/index)) — Name of the table.
* `engine` ([String](/reference/data-types/index)) — Name of the table engine without parameters.
* `disk_name` ([String](/reference/data-types/index)) — Name of a disk that stores the data part.
* `path` ([String](/reference/data-types/index)) — Absolute path to the folder with data part files.
* `column` ([String](/reference/data-types/index)) — Name of the column.
* `type` ([String](/reference/data-types/index)) — Column type.
* `column_position` ([UInt64](/reference/data-types/index)) — Ordinal position of a column in a table starting with 1.
* `default_kind` ([String](/reference/data-types/index)) — Expression type (DEFAULT, MATERIALIZED, ALIAS) for the default value, or an empty string if it is not defined.
* `default_expression` ([String](/reference/data-types/index)) — Expression for the default value, or an empty string if it is not defined.
* `column_bytes_on_disk` ([UInt64](/reference/data-types/index)) — Total size of the column in bytes.
* `column_data_compressed_bytes` ([UInt64](/reference/data-types/index)) — Total size of the compressed data in the column, in bytes.
* `column_data_uncompressed_bytes` ([UInt64](/reference/data-types/index)) — Total size of the decompressed data in the column, in bytes.
* `column_marks_bytes` ([UInt64](/reference/data-types/index)) — The size of the marks for column, in bytes.
* `column_modification_time` ([Nullable(DateTime)](/reference/data-types/index)) — The last time the column was modified.
* `column_ttl_min` ([Nullable(DateTime)](/reference/data-types/index)) — The minimum value of the calculated TTL expression of the column.
* `column_ttl_max` ([Nullable(DateTime)](/reference/data-types/index)) — The maximum value of the calculated TTL expression of the column.
* `statistics` ([Array(String)](/reference/data-types/index)) — The statistics of the column.
* `estimates.min` ([Nullable(String)](/reference/data-types/index)) — Estimated minimum value of the column.
* `estimates.max` ([Nullable(String)](/reference/data-types/index)) — Estimated maximum value of the column.
* `estimates.cardinality` ([Nullable(UInt64)](/reference/data-types/index)) — Estimated cardinality of the column.
* `estimates.null_count` ([Nullable(UInt64)](/reference/data-types/index)) — Estimated number of NULL values in the column.
* `serialization_kind` ([String](/reference/data-types/index)) — Kind of serialization of a column
* `substreams` ([Array(String)](/reference/data-types/index)) — Names of substreams to which column is serialized
* `filenames` ([Array(String)](/reference/data-types/index)) — Names of files for each substream of a column respectively
* `subcolumns.names` ([Array(String)](/reference/data-types/index)) — Names of subcolumns of a column
* `subcolumns.types` ([Array(String)](/reference/data-types/index)) — Types of subcolumns of a column
* `subcolumns.serializations` ([Array(String)](/reference/data-types/index)) — Kinds of serialization of subcolumns of a column
* `subcolumns.bytes_on_disk` ([Array(UInt64)](/reference/data-types/index)) — Sizes in bytes for each subcolumn
* `subcolumns.data_compressed_bytes` ([Array(UInt64)](/reference/data-types/index)) — Sizes of the compressed data for each subcolumn, in bytes
* `subcolumns.data_uncompressed_bytes` ([Array(UInt64)](/reference/data-types/index)) — Sizes of the decompressed data for each subcolumn, in bytes
* `subcolumns.marks_bytes` ([Array(UInt64)](/reference/data-types/index)) — Sizes of the marks for each subcolumn of a column, in bytes

<h2 id="example">
  Example
</h2>

```sql theme={null}
SELECT * FROM system.parts_columns LIMIT 1 FORMAT Vertical;
```

```text theme={null}
Row 1:
──────
partition:                             tuple()
name:                                  all_1_2_1
part_type:                             Wide
active:                                1
marks:                                 2
rows:                                  2
bytes_on_disk:                         155
data_compressed_bytes:                 56
data_uncompressed_bytes:               4
marks_bytes:                           96
modification_time:                     2020-09-23 10:13:36
remove_time:                           2106-02-07 06:28:15
refcount:                              1
min_date:                              1970-01-01
max_date:                              1970-01-01
partition_id:                          all
min_block_number:                      1
max_block_number:                      2
level:                                 1
data_version:                          1
primary_key_bytes_in_memory:           2
primary_key_bytes_in_memory_allocated: 64
database:                              default
table:                                 53r93yleapyears
engine:                                MergeTree
disk_name:                             default
path:                                  /var/lib/clickhouse/data/default/53r93yleapyears/all_1_2_1/
column:                                id
type:                                  Int8
column_position:                       1
default_kind:
default_expression:
column_bytes_on_disk:                  76
column_data_compressed_bytes:          28
column_data_uncompressed_bytes:        2
column_marks_bytes:                    48
```

<h2 id="see-also">
  See Also
</h2>

* [MergeTree family](/reference/engines/table-engines/mergetree-family/mergetree)
* [Calculating the number and size of compact and wide parts](/resources/support-center/knowledge-base/troubleshooting/count-parts-by-type)