Describe statement doesn't work for index alias

[dai-chen]

When DESCRIBE statement is used against an index alias, no result is returned.

PUT dropdown-region-marketplace
{
  "mappings": {
    "properties": {
      "balance": {
        "type": "float"
      },
      "age": {
        "type": "integer"
      }
    }
  }
}

# Work without issue
POST _opendistro/_sql
{
  "query": "DESCRIBE TABLES LIKE dropdown-region-marketplace"
}

# Empty result returned
PUT /dropdown-region-marketplace/_alias/ddregionmarketplace
POST _opendistro/_sql
{
  "query": "DESCRIBE TABLES LIKE ddregionmarketplace"
}
{
 ...
  "total": 0,
  "datarows": [],
  "size": 0,
  "status": 200
}

[dai-chen]

I debugged code and found that we tried to match the index name returned in ES get mapping API and pattern in query. In the case of index alias, index name rather than alias is returned in get mapping API response. Thus it is unable to match the original pattern text in query.

sql/legacy/src/main/java/com/amazon/opendistroforelasticsearch/sql/legacy/executor/format/DescribeResultSet.java

Line 99 in 35e37a3

if (matchesPattern(index, statement.getIndexPattern())) {