# COLUMNS > Provides detailed information about columns in tables, including column names, data types, default values, and other attributes. # COLUMNS The `COLUMNS` provides detailed information about columns in tables. ```sql USE INFORMATION_SCHEMA; DESC COLUMNS; ``` The output is as follows: ```sql +--------------------------+--------+------+------+---------+---------------+ | Column | Type | Key | Null | Default | Semantic Type | +--------------------------+--------+------+------+---------+---------------+ | table_catalog | String | | NO | | FIELD | | table_schema | String | | NO | | FIELD | | table_name | String | | NO | | FIELD | | column_name | String | | NO | | FIELD | | ordinal_position | Int64 | | NO | | FIELD | | character_maximum_length | Int64 | YES | | FIELD | | character_octet_length | Int64 | YES | | FIELD | | numeric_precision | Int64 | YES | | FIELD | | numeric_scale | Int64 | YES | | FIELD | | datetime_precision | Int64 | YES | | FIELD | | character_set_name | String | | YES | | FIELD | | collation_name | String | | YES | | FIELD | | column_key | String | | NO | | FIELD | | extra | String | | NO | | FIELD | | privileges | String | | NO | | FIELD | | generation_expression | String | | NO | | FIELD | | greptime_data_type | String | | NO | | FIELD | | data_type | String | | NO | | FIELD | | semantic_type | String | | NO | | FIELD | | column_default | String | | YES | | FIELD | | is_nullable | String | | NO | | FIELD | | column_type | String | | NO | | FIELD | | column_comment | String | | YES | | FIELD | | srs_id | Int64 | | YES | | FIELD | +--------------------------+--------+------+------+---------+---------------+ 24 rows in set (0.00 sec) ``` Create a table `public.t1` and query the information in the `COLUMNS` table: ```sql CREATE TABLE public.t1 (h STRING, v FLOAT64, ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP() TIME INDEX, PRIMARY KEY(h)); SELECT * FROM COLUMNS WHERE table_schema='public' AND TABLE_NAME='t1'\G ``` The output is as follows: ```sql *************************** 1. row *************************** table_catalog: greptime table_schema: public table_name: t1 column_name: h ordinal_position: 1 character_maximum_length: 2147483647 character_octet_length: 2147483647 numeric_precision: NULL numeric_scale: NULL datetime_precision: NULL character_set_name: utf8 collation_name: utf8_bin column_key: PRI extra: privileges: select,insert generation_expression: greptime_data_type: String data_type: string semantic_type: TAG column_default: NULL is_nullable: Yes column_type: string column_comment: NULL srs_id: NULL *************************** 2. row *************************** table_catalog: greptime table_schema: public table_name: t1 column_name: v ordinal_position: 2 character_maximum_length: NULL character_octet_length: NULL numeric_precision: 22 numeric_scale: NULL datetime_precision: NULL character_set_name: NULL collation_name: NULL column_key: extra: privileges: select,insert generation_expression: greptime_data_type: Float64 data_type: double semantic_type: FIELD column_default: NULL is_nullable: Yes column_type: double column_comment: NULL srs_id: NULL *************************** 3. row *************************** table_catalog: greptime table_schema: public table_name: t1 column_name: ts ordinal_position: 3 character_maximum_length: NULL character_octet_length: NULL numeric_precision: NULL numeric_scale: NULL datetime_precision: 3 character_set_name: NULL collation_name: NULL column_key: TIME INDEX extra: privileges: select,insert generation_expression: greptime_data_type: TimestampMillisecond data_type: timestamp(3) semantic_type: TIMESTAMP column_default: current_timestamp() is_nullable: No column_type: timestamp(3) column_comment: NULL srs_id: NULL 3 rows in set (0.03 sec) ``` The description of columns in the `COLUMNS` table is as follows: - `table_catalog`: The name of the catalog to which the table with the column belongs. The value is always `greptime` in OSS project. - `table_schema`: The name of the database in which the table with the column is located. - `table_name`: The name of the table with the column. - `column_name`: The name of the column. - `ordinal_position`: The position of the column in the table. - `character_maximum_length`: For string columns, the maximum length in characters. - `character_octet_length`: For string columns, the maximum length in bytes. - `numeric_precision`: The precision of the column for numeric data types. - `numeric_scale`: The scale of the column for numeric data types. - `datetime_precision`: The fractional seconds precision of the column for datetime data types. - `character_set_name`: The name of the character set of a string column. - `collation_name`: The name of the collation of a string column. - `column_key`: The key type of the column. It can be one of the following: `PRI`, `TIME INDEX`, or an empty string. - `extra`: Additional information about the column. - `privileges`: The privilege that the current user has on this column. - `generation_expression`: For generated columns, this value displays the expression used to calculate the column value. For non-generated columns, the value is empty. - `greptime_data_type`: The GreptimeDB [data type](/reference/sql/data-types.md) of the column. - `data_type`: The type of data in the column. - `semantic_type`: The type of the column. It can be one of the following: `TAG`, `FIELD`, or `TIMESTAMP`. - `column_default`: The default value of the column. If the explicit default value is `NULL`, or if the column definition does not include the `default` clause, this value is `NULL`. - `is_nullable`: Whether the column is nullable. If the column can store null values, this value is `YES`; otherwise, it is `NO`. - `column_type`: The data type of the column. It is the same as the `DATA_TYPE` column. - `column_comment`: Comments contained in the column definition. - `srs_id`: The ID of the spatial reference system (SRS) of the column. The corresponding `SHOW` statement is as follows: ```sql SHOW COLUMNS FROM t1 FROM public; ``` The output is as follows: ```sql +-------+--------------+------+------------+---------------------+-------+----------------------+ | Field | Type | Null | Key | Default | Extra | Greptime_type | +-------+--------------+------+------------+---------------------+-------+----------------------+ | h | string | Yes | PRI | NULL | | String | | ts | timestamp(3) | No | TIME INDEX | current_timestamp() | | TimestampMillisecond | | v | double | Yes | | NULL | | Float64 | +-------+--------------+------+------------+---------------------+-------+----------------------+ 3 rows in set (0.01 sec) ```