Function removeRedundantFromClause

packages/db/src/query/optimizer.ts:471–502

* Removes redundant subqueries from a FROM clause. * * @param from - The FROM clause to process * @returns A FROM clause with redundant subqueries removed

(from: From)

 * @returns A FROM clause with redundant subqueries removed
 */
function removeRedundantFromClause(from: From): From {
  if (from.type === `unionFrom`) {
    return new UnionFromClass(
      from.sources.map((source) => removeRedundantFromClause(source) as any),
    )
  }

  if (from.type === `unionAll`) {
    return new UnionAllClass(
      from.queries.map((branch) => removeRedundantSubqueries(branch)),
    )
  }

  if (from.type === `collectionRef`) {
    return from
  }

  const processedQuery = removeRedundantSubqueries(from.query)

  // Check if this subquery is redundant
  if (isRedundantSubquery(processedQuery)) {
    // Return the inner query's FROM clause with this alias
    const innerFrom = removeRedundantFromClause(processedQuery.from)
    if (innerFrom.type === `collectionRef`) {
      return new CollectionRefClass(innerFrom.collection, from.alias)
    } else if (innerFrom.type === `queryRef`) {
      return new QueryRefClass(innerFrom.query, from.alias)
    }
  }

  return new QueryRefClass(processedQuery, from.alias)
}

function removeRedundantJoinFromClause(
  from: CollectionRefClass | QueryRefClass,