Contains information about columns in all the tables.
You can use this table to get information similar to the [DESCRIBE TABLE](../../sql-reference/statements/misc.md#misc-describe-table) query, but for multiple tables at once.
The `system.columns` table contains the following columns (the column type is shown in brackets):
-`database` (String) — Database name.
-`table` (String) — Table name.
-`name` (String) — Column name.
-`type` (String) — Column type.
-`default_kind` (String) — Expression type (`DEFAULT`, `MATERIALIZED`, `ALIAS`) for the default value, or an empty string if it is not defined.
-`default_expression` (String) — Expression for the default value, or an empty string if it is not defined.
-`data_compressed_bytes` (UInt64) — The size of compressed data, in bytes.
-`data_uncompressed_bytes` (UInt64) — The size of decompressed data, in bytes.
-`marks_bytes` (UInt64) — The size of marks, in bytes.
-`comment` (String) — Comment on the column, or an empty string if it is not defined.
-`is_in_partition_key` (UInt8) — Flag that indicates whether the column is in the partition expression.
-`is_in_sorting_key` (UInt8) — Flag that indicates whether the column is in the sorting key expression.
-`is_in_primary_key` (UInt8) — Flag that indicates whether the column is in the primary key expression.
-`is_in_sampling_key` (UInt8) — Flag that indicates whether the column is in the sampling key expression.
