[BUG] unsupported operator: if when using sql API

What is the bug?
Opensearch version 2.8.0
we are migrating from elasticsearch to opensearch and planning to use nested sql queries to replace runtime field which were supported in elasticsearch sql API

after following documentation from https://opensearch.org/docs/2.0/search-plugins/sql/sql-ppl-api/#query-api

when I try to run sql query using if operator I get following exception
{
"error": {
"reason": "There was internal problem at backend",
"details": "unsupported operator: if",
"type": "UnsupportedOperationException"
},
"status": 503
}

same query works in query workbench. if I use nested query only group by fields are returned.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. call _sql API to run query in jdbc format
2. post sql query
3. go to query workbench and verify query works

steps to replicate in dev console (queries works workbench)

POST _bulk
{ "index" : { "_index" : "test_bulk1", "_id" : "1" } }
{ "a": "a", "id": 1 }



GET test_bulk1/_search


POST /_plugins/_sql?format=jdbc
{
  "query": "SELECT IF(id=1, 1, 0 ) as id FROM test_bulk1    group by a",
  "fetch_size" : 10
}

POST /_plugins/_sql?format=jdbc
{
  "query": "SELECT *FROM (SELECT IF(id=1, 1, 0 ) as id FROM test_bulk1 group by a)as tmp",
  "fetch_size" : 10
}

What is the expected behavior?
output from query workbench and SQL needs to be consistent

What is your host/environment?

• OS: Centos 7
• Opensearch Version 2.8.0
• Plugins

Do you have any screenshots?
N/A
Do you have any additional context?
N/A

Start by reproducing the JDBC-formatted requests to /_plugins/_sql with the provided bulk data and IF queries, then compare them with the query workbench behavior. Trace the SQL API handling of nested queries and the IF operator; done means equivalent results are returned consistently instead of an unsupported-operator error.