# Rationale
Accessing the list of columns via `select * from information_schema.columns` (introduced in #9840) is a lot to type

See the doc for background: https://docs.google.com/document/d/12cpZUSNPqVH9Z0BBx6O8REu7TFqL-NPPAYCUPpDls1k/edit#

This is a sister PR to `SHOW TABLES` here:  #9847

# Proposal

Add support for `SHOW COLUMNS FROM <table>` command.

Following the MySQL syntax supported by sqlparser: https://dev.mysql.com/doc/refman/8.0/en/show-columns.html

# Example Use

Setup:
```
echo "1,Foo,44.9" > /tmp/table.csv
echo "2,Bar,22.1" >> /tmp/table.csv
cargo run --bin datafusion-cli
```

Then run :

```
> CREATE EXTERNAL TABLE t(a int, b varchar, c float)
STORED AS CSV
LOCATION '/tmp/table.csv';

 0 rows in set. Query took 0 seconds.

> show columns from t;
+---------------+--------------+------------+-------------+-----------+-------------+
| table_catalog | table_schema | table_name | column_name | data_type | is_nullable |
+---------------+--------------+------------+-------------+-----------+-------------+
| datafusion    | public       | t          | a           | Int32     | NO          |
| datafusion    | public       | t          | b           | Utf8      | NO          |
| datafusion    | public       | t          | c           | Float32   | NO          |
+---------------+--------------+------------+-------------+-----------+-------------+
3 row in set. Query took 0 seconds.
```

# Commentary

Note that the identifiers are case sensitive (which is a more general
problem that affects all name resolution, not just `SHOW COLUMNS`). Ideally this should also work:

```
> show columns from T;
Plan("Unknown relation for SHOW COLUMNS: T")

> select * from T;
Plan("Table or CTE with name \'T\' not found")
```

Closes #9866 from alamb/alamb/show_columns

Authored-by: Andrew Lamb <[email protected]>
Signed-off-by: Andrew Lamb <[email protected]>

# Rationale
Accessing the list of columns via `select * from information_schema.columns` (introduced in apache#9840) is a lot to type

See the doc for background: https://docs.google.com/document/d/12cpZUSNPqVH9Z0BBx6O8REu7TFqL-NPPAYCUPpDls1k/edit#

This is a sister PR to `SHOW TABLES` here:  apache#9847

# Proposal

Add support for `SHOW COLUMNS FROM <table>` command.

Following the MySQL syntax supported by sqlparser: https://dev.mysql.com/doc/refman/8.0/en/show-columns.html

# Example Use

Setup:
```
echo "1,Foo,44.9" > /tmp/table.csv
echo "2,Bar,22.1" >> /tmp/table.csv
cargo run --bin datafusion-cli
```

Then run :

```
> CREATE EXTERNAL TABLE t(a int, b varchar, c float)
STORED AS CSV
LOCATION '/tmp/table.csv';

 0 rows in set. Query took 0 seconds.

> show columns from t;
+---------------+--------------+------------+-------------+-----------+-------------+
| table_catalog | table_schema | table_name | column_name | data_type | is_nullable |
+---------------+--------------+------------+-------------+-----------+-------------+
| datafusion    | public       | t          | a           | Int32     | NO          |
| datafusion    | public       | t          | b           | Utf8      | NO          |
| datafusion    | public       | t          | c           | Float32   | NO          |
+---------------+--------------+------------+-------------+-----------+-------------+
3 row in set. Query took 0 seconds.
```

# Commentary

Note that the identifiers are case sensitive (which is a more general
problem that affects all name resolution, not just `SHOW COLUMNS`). Ideally this should also work:

```
> show columns from T;
Plan("Unknown relation for SHOW COLUMNS: T")

> select * from T;
Plan("Table or CTE with name \'T\' not found")
```

Closes apache#9866 from alamb/alamb/show_columns

Authored-by: Andrew Lamb <[email protected]>
Signed-off-by: Andrew Lamb <[email protected]>