[CALCITE-7196] Create an optimization pass which can convert some cases of Correlate + Unnest to Unnest

[mihaibudiu]

https://issues.apache.org/jira/browse/CALCITE-7196

[xiedeyantu]

I don't know much about this, but the test results look good. So I'm just offering some simple suggestions for your reference. It would be great if someone else could review them.

[xiedeyantu]

I think we can add a test case constructed in a non-Values ​​manner. Like the one below, I tested your code and it looks good.

  @Test void testUnnestDecorrelate4() {
    final String sql = "select t2.ename\n"
        + "from DEPT_NESTED as t1,\n"
        + "unnest(t1.employees) as t2";
    sql(sql)
        .withPreRule(CoreRules.PROJECT_REMOVE)
        .withRule(CoreRules.UNNEST_DECORRELATE)
        .check();
  }

Xml result:

  <TestCase name="testUnnestDecorrelate4">
    <Resource name="sql">
      <![CDATA[select t2.ename
from DEPT_NESTED as t1,
unnest(t1.employees) as t2]]>
    </Resource>
    <Resource name="planBefore">
      <![CDATA[
LogicalProject(ENAME=[$5])
  LogicalCorrelate(correlation=[$cor0], joinType=[inner], requiredColumns=[{3}])
    LogicalTableScan(table=[[CATALOG, SALES, DEPT_NESTED]])
    Uncollect
      LogicalProject(EMPLOYEES=[$cor0.EMPLOYEES])
        LogicalValues(tuples=[[{ 0 }]])
]]>
    </Resource>
    <Resource name="planAfter">
      <![CDATA[
LogicalProject(ENAME=[$1])
  Uncollect
    LogicalProject(EMPLOYEES=[$3])
      LogicalTableScan(table=[[CATALOG, SALES, DEPT_NESTED]])
]]>
    </Resource>
  </TestCase>

[xiedeyantu]

A small suggestion. It seems that all the operations related to the builder can be linked together in a point-like manner.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
88.5% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[dssysolyatin]

What about embedded RexFieldAccess ?

 final String sql = "WITH t1 AS (SELECT ROW(ARRAY[1, 2, 3]) as struct_with_array_field)\n"
        + "SELECT array_element.id\n"
        + "FROM t1, UNNEST(t1.struct_with_array_field.EXPR$0) AS array_element(id)";
    sql(sql)
        .withRule(CoreRules.UNNEST_PROJECT_DECORRELATE)
        .check();