Allow where clause in subgraph queries to reference another field in type

Do you want to request a feature or report a bug?

Feature

What is the current behavior?

Currently, the where clause in a subgraph query only allows you to pass values to it that are of the type of the field being filtered against.

ex:

query Indexers {
  indexers(where: { stakedTokens: 0 }) {
    id
    stakedTokens
    lockedTokens
  }
}

Where: stakedTokens is of type BigInt and the value passed (0 in the example) must also be a BigInt.

What is the expected behavior?

It would be very helpful if the where clause was able to compare two fields against each other to filter results.

ex:

query Indexers {
  indexers(where: { stakedTokens: {indexer? me? this?}.lockedTokens }) {
    id
    stakedTokens
    lockedTokens
  }
}

Mapping down to sql, this would look (something like):

SELECT id, staked_tokens, locked_tokens FROM indexer WHERE staked_tokens = locked_tokens;

Start by tracing how GraphQL subgraph where clauses are parsed and translated to SQL; the issue names no implementation files or tests. Define the field-to-field comparison syntax and identify the query and database layers that would need support, then add coverage for comparing stakedTokens with lockedTokens.