sql: fix "descriptor not found" error when dropping a database with t…

[ajwerner]

…emp views

The bug here is that there are cases in drop database cascade where we'll
attempt to qualify the name of a view involved in a cascaded drop that is
not part of the current session's temporary schema. In that scenario, we
don't know the schema except by its ID. The temporary schemas do not have
descriptors, only namespace entries.

We could do something different like delete all of the views first but that
won't help for the backport PR we need to make as we only carry prefix
descriptors around in master.

Release note (bug fix): Fixed a bug where DROP DATABASE could return errors
if the database contained temporary views in use in an another session.

[cockroach-teamcity]

This change is 

[mgartner]

Thanks for the quick fix!

Reviewed 2 of 2 files at r1.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @ajwerner)

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pkg/sql/logictest/testdata/logic_test/temp_table, line 305 at r1 (raw file):

CREATE TABLE not_temp (i INT PRIMARY KEY);
CREATE TEMPORARY TABLE "testuser_tmp" (i INT PRIMARY KEY);
CREATE TEMPORARY VIEW "tempuser_view" AS SELECT i FROM testuser_tmp;

nit: is there a need for the "s?

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pkg/sql/logictest/testdata/logic_test/temp_table, line 327 at r1 (raw file):

			),
			'pg_temp_[^.]+.',
			'pg_temp.'

nit: replace tabs with spaces and align SELECT

[mgartner]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! 0 of 0 LGTMs obtained (and 1 stale) (waiting on @ajwerner)

[ajwerner]

TFTR

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)