sql: Error messages should be improved in case of no matching data source

[rytaft]

Consider the following invalid query:

root@:26257/> select count(tpch.nation.n_nationkey) from tpch.customer c, tpch.public.nation n where tpch.public.customer.c_nationkey = nation.n_nationkey group by tpch.public.nation.n_nationkey limit 10;

The error that CockroachDB returns for this query is:

pq: no data source matches prefix: tpch.public.customer

PostgreSQL has a friendlier error message with a hint:

Postgres: ERROR: invalid reference to FROM-clause entry for table "nation" Hint: Perhaps you meant to reference the table alias "n". Position: 14

[knz]

I'll look what I can do. Note that I never like pg's error message that refers to a "FROM" clause, because it can also appear when there is no FROM clause whatsoever.

Meanwhile I'll just ignore pg's hint for now, since it's complex to implement we're not going to keep the current lookup code anyway.

But Becca I do have a hint for you: the object pgerror.Error has a SetHint method. I encourage you to implement any hint you'd like in the lookup code you recently implemented.

[rytaft]

Sounds good - thanks!

[knz]

Fixed in #27396.