> ## Documentation Index > Fetch the complete documentation index at: https://private-7c7dfe99-mintlify-fbfa8bee.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. > System table containing information about columns in projection parts for tables of the MergeTree family # system.projection_parts_columns

Description

This table contains information about columns in projection parts for tables of the MergeTree family.

Columns

* `partition` ([String](/reference/data-types/index)) — The partition name. * `name` ([String](/reference/data-types/index)) — Name of the data part. * `part_type` ([String](/reference/data-types/index)) — The data part storing format. * `parent_name` ([String](/reference/data-types/index)) — The name of the source (parent) data part. * `parent_uuid` ([UUID](/reference/data-types/index)) — The UUID of the source (parent) data part. * `parent_part_type` ([String](/reference/data-types/index)) — The source (parent) data part storing format. * `active` ([UInt8](/reference/data-types/index)) — Flag that indicates whether the data part is active * `marks` ([UInt64](/reference/data-types/index)) — The number of marks. * `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. * `parent_marks` ([UInt64](/reference/data-types/index)) — The number of marks in the source (parent) part. * `parent_rows` ([UInt64](/reference/data-types/index)) — The number of rows in the source (parent) part. * `parent_bytes_on_disk` ([UInt64](/reference/data-types/index)) — Total size of all the source (parent) data part files in bytes. * `parent_data_compressed_bytes` ([UInt64](/reference/data-types/index)) — Total size of compressed data in the source (parent) data part. * `parent_data_uncompressed_bytes` ([UInt64](/reference/data-types/index)) — Total size of uncompressed data in the source (parent) data part. * `parent_marks_bytes` ([UInt64](/reference/data-types/index)) — The size of the file with marks in the source (parent) data part. * `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 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 column with marks, in bytes. * `column_modification_time` ([Nullable(DateTime)](/reference/data-types/index)) — The last time the column was modified.