Fix back quoted alias of FROM subquery

[dai-chen]

Description

Previously, FROM subquery alias was not unquoted in AST layer. This caused back quoted symbol name pushed to symbol table and thus fall back to legacy subquery logic due to semantic exception.

Example

Take SELECT `a`.`name` FROM (...) AS `a` for example. In AST node, alias name of RelationSubquery is still `a` and then Analyzer push `a` to symbol table. When resolving a in a.name, semantic exception is thrown because there is `a` instead of a in symbol table. Please check the comments in #550 below for more details.

Testing

The comparison test seems broken due to failed OpenSearch address resolving. I made local changes and ran it manually. Need to send separate PR to fix the comparison test framework.

$ ./gradlew :integ-test:comparisonTest -Dqueries=bugfixes/550.txt

...
{
  "summary": {
    "total": 2,
    "failure": 0,
    "success": 2
  },
  "tests": [
    {
      "result": "Success",
      "id": 1,
      "sql": "SELECT ABS(`flights`.`AvgTicketPrice`) FROM (SELECT `AvgTicketPrice` FROM `opensearch_dashboards_sample_data_flights`) AS `flights` GROUP BY ABS(`flights`.`AvgTicketPrice`)"
    },
    {
      "result": "Success",
      "id": 2,
      "sql": "SELECT `b`.`Origin`, `b`.`avgPrice` FROM (SELECT `a`.`Origin` AS `Origin`, AVG(`AvgTicketPrice`) AS `avgPrice` FROM (SELECT `Origin`, `AvgTicketPrice` FROM `opensearch_dashboards_sample_data_flights` WHERE `FlightDelay` = True) AS `a` GROUP BY `a`.`Origin`) AS `b` ORDER BY `b`.`avgPrice` DESC"
    }
  ]
}

Documentation

I don't see the limitation mentioned in our doc any more. Even very complex and nested subquery as below can be supported now. So I updated the doc to remove the limitation statement.

POST _plugins/_sql
{
  "query": """
    SELECT b.Origin, b.avgPrice
    FROM (
      SELECT
        a.Origin AS Origin,
        AVG(AvgTicketPrice) AS avgPrice
      FROM (
        SELECT Origin, AvgTicketPrice
        FROM opensearch_dashboards_sample_data_flights
        WHERE FlightDelay = True
      ) AS a
      GROUP BY a.Origin
    ) AS b
    ORDER BY b.avgPrice DESC
  """
}

{
  "schema": [
    {
      "name": "Origin",
      "type": "keyword"
    },
    {
      "name": "avgPrice",
      "type": "double"
    }
  ],
  "datarows": [
    [
      "Charles de Gaulle International Airport",
      999.1396484375
    ],
    [
      "Huntsville International Carl T Jones Field",
      993.1741333007812
    ],
    [
      "Minneapolis-St Paul International/Wold-Chamberlain Airport",
      952.474853515625
    ],
...

Explain output:
{
  "root": {
    "name": "ProjectOperator",
    "description": {
      "fields": "[Origin, avgPrice]"
    },
    "children": [
      {
        "name": "SortOperator",
        "description": {
          "sortList": {
            "avgPrice": {
              "sortOrder": "DESC",
              "nullOrder": "NULL_LAST"
            }
          }
        },
        "children": [
          {
            "name": "ProjectOperator",
            "description": {
              "fields": "[Origin, avgPrice]"
            },
            "children": [
              {
                "name": "AggregationOperator",
                "description": {
                  "aggregators": "[AVG(AvgTicketPrice)]",
                  "groupBy": "[Origin]"
                },
                "children": [
                  {
                    "name": "ProjectOperator",
                    "description": {
                      "fields": "[Origin, AvgTicketPrice]"
                    },
                    "children": [
                      {
                        "name": "OpenSearchIndexScan",
                        "description": {
                          "request": """OpenSearchQueryRequest(indexName=opensearch_dashboards_sample_data_flights, sourceBuilder={"from":0,"size":200,"timeout":"1m","query":{"term":{"FlightDelay":{"value":true,"boost":1.0}}},"_source":{"includes":["Origin","AvgTicketPrice"],"excludes":[]},"sort":[{"_doc":{"order":"asc"}}]}, searchDone=false)"""
                        },
                        "children": []
                      }
                    ]
                  }
                ]
              }
            ]
          }
        ]
      }
    ]
  }
}

Issues Resolved

• Root cause analysis: [BUG] Subquery aliasing doesn't work with ` characters #550
• Issues probably related:
  • Lack of support for subqueries results in RuntimeException[BUG] #304
  • Group By results in RuntimeException[BUG] #342
  • [BUG] A query with a subquery fails #347

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov-commenter]

Codecov Report

Merging #1189 (1d36d7a) into main (034027c) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #1189      +/-   ##
============================================
- Coverage     95.81%   95.81%   -0.01%     
  Complexity     3521     3521              
============================================
  Files           352      352              
  Lines          9359     9358       -1     
  Branches        673      673              
============================================
- Hits           8967     8966       -1     
  Misses          334      334              
  Partials         58       58              

Flag	Coverage Δ
query-workbench	62.76% <ø> (ø)
sql-engine	98.31% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...java/org/opensearch/sql/sql/parser/AstBuilder.java	100.00% <100.00%> (ø)
...pensearch/sql/ppl/parser/AstExpressionBuilder.java	100.00% <0.00%> (ø)

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