Modify the implementation of `Explorer.Chain.where_transaction_has_multiple_internal_transactions`

Problem: the implementation of that `WHERE` filter is too inefficient.
In particular this was brought to attention because it causes `Explorer.Etherscan.list_internal_transactions/2` to timeout for some addresses.
(For example: address `0x1B3858E01CCE5d0491f3c96A9996a65607f3493b`)

Solution: while keeping the same result the previous check for siblings (SELECT/LIMIT 2/COUNT/(> 1)) has been replaced by a less expensive one that better uses the existing indexes (EXISTS/index comparison).

CHANGELOG.md

@@ -57,6 +57,7 @@
 - [#2204](https://github.com/poanetwork/blockscout/pull/2204) - fix large contract verification
 - [#2247](https://github.com/poanetwork/blockscout/pull/2247) - hide logs search if there are no logs
 - [#2248](https://github.com/poanetwork/blockscout/pull/2248) - sort block after query execution for average block time
+- [#2267](https://github.com/poanetwork/blockscout/pull/2267) - Modify implementation of `where_transaction_has_multiple_internal_transactions`
 
 ### Chore
 - [#2127](https://github.com/poanetwork/blockscout/pull/2127) - use previouse chromedriver version

apps/explorer/lib/explorer/chain.ex

@@ -2580,14 +2580,14 @@ defmodule Explorer.Chain do
       internal_transaction.type != ^:call or
         fragment(
           """
-          (SELECT COUNT(sibling.*)
+          EXISTS (SELECT sibling.*
           FROM internal_transactions AS sibling
-          WHERE sibling.transaction_hash = ?
+          WHERE sibling.transaction_hash = ? AND sibling.index != ?
-          LIMIT 2
           )
           """,
-          transaction.hash
+          transaction.hash,
-        ) > 1
+          internal_transaction.index
+        )
     )
   end