sql: support writes to columns added in a transaction

[ajwerner]

This issue is being peeled out as a sub-issue of #42061, specifically around the problem and proposal put forth in this comment: #42061 (comment).

Please refer to the above comment for a bunch of commentary. The short summary is that columns added to tables using ALTER TABLE ... ADD COLUMN statements in a transaction are not available for use after that statement in the same transaction. Postgres permits immediate use of the new column.

Relates to #40862

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I'll move content from the referenced thread into this issue as it settles.

Jira issue: CRDB-5300

[devadvocado]

Ran into this issue when testing UDFs in 22.2

demo@127.0.0.1:26257/movr> BEGIN;
BEGIN


Time: 0ms total (execution 0ms / network 0ms)

demo@127.0.0.1:26257/movr  OPEN> ALTER TABLE users ADD COLUMN is_awesome BOOL DEFAULT true;
ALTER TABLE
Time: 7ms total (execution 7ms / network 0ms)

demo@127.0.0.1:26257/movr  OPEN> CREATE FUNCTION areyouawesome(boolean) RETURNS int AS $$                                                                                                                                     SELECT COUNT(is_awesome) FROM users WHERE is_awesome = $1;                                                    $$ LANGUAGE SQL;
ERROR: column "is_awesome" does not exist
SQLSTATE: 42703
demo@127.0.0.1:26257/? ERROR>

[ajwerner]

This is a major motivation for https://github.com/cockroachdb/cockroach/blob/master/docs/RFCS/20200909_transactional_schema_changes.md. It's a hard problem.