Insertion to temporary table doesn't work

[VladTheJunior]

Example https://github.com/ClickHouse/clickhouse-rs/blob/main/examples/session_id.rs returns SchemaMismatch("While processing struct MyRow: database schema has no column named i.\n#### All struct fields:\n- i\n#### All schema columns:\n")

Edit: It works with disabled validation

[abonander]

It looks like the problem is this query:

clickhouse-rs/src/lib.rs

Lines 592 to 597 in 7891e8b

	let mut out = "SELECT \
	name, \
	type, \
	default_kind \
	FROM system.columns \
	WHERE database = "

In the documentation for the system.columns view: https://clickhouse.com/docs/operations/system-tables/columns

Columns from temporary tables are visible in the system.columns only in those session where they have been created. They are shown with the empty database field.

A simple fix to the query would be to allow the database column to be empty.

I worry about a possible ambiguity if you create a temporary table with the same name as a permanent one in the current database, which would cause this query to return data for both tables. But I suppose in that case, the INSERT query would fail.

We could instead change this to a DESCRIBE TABLE statement which should go through the same name resolution codepath as the INSERT statement would.