[CALCITE-7689] MAP equality compares maps by insertion order

[mihaibudiu]

Jira Link

CALCITE-7689

Changes Proposed

Two MAP values should be equal when they have the same exact key and each key maps to the same exact value. Key and value comparisons use <=> (IS NOT DISTINCT FROM), consistent with ARRAY values.

As a side-effect this changes ordering of maps too.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
88.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[xiedeyantu]

I checked the SQL standard, and there are no constraints regarding how maps should be compared; I believe any implementation approach we choose would be justifiable. However, I have observed that both DuckDB and ClickHouse return false when executing select map('a', 1, 'b', 2) = map('b', 2, 'a', 1). I am unsure what the best approach for Calcite would be.

[mihaibudiu]

Clickhouse maps are actually not even maps, since they can have duplicate keys.
They are stored as Array(Tuple(K, V)).
https://clickhouse.com/docs/reference/data-types/map
So their semantics is not a good fit for Calcite.

[xiedeyantu]

Although the databases or query engines I am familiar with typically treat map comparisons as order-dependent, and I had previously hesitated regarding the implementation approach, I personally support the implementation in this PR. If no one raises an objection, I think it is acceptable, as it aligns better with intuition.

[mihaibudiu]

Let's see if there are any other objections.