db-sync: Fix pool_id column in reward table

The 'pool_id' in the 'reward' table is obtained by querying the
'delegation' table, and that query ordered the results by
'active_epoch_no'. However, for the case where two delegation (or
pool update) certificates for the same address (or pool) are
registered in the same epoch, this query can be incorrect.

The fix is join with the 'block' table and order by the descending
value of the 'slot_no' field.

Closes: #361

cardano-db-sync/src/Cardano/DbSync/Era/Shelley/Query.hs

@@ -62,21 +62,29 @@ queryStakeAddress addr = do
 -- query catches this situation.
 queryStakeAddressAndPool :: MonadIO m => Word64 -> ByteString -> ReaderT SqlBackend m (Either LookupFail (StakeAddressId, PoolHashId))
 queryStakeAddressAndPool epoch addr = do
-    res <- select . from $ \ (saddr `InnerJoin` dlg) -> do
+    res <- select . from $ \ (saddr `InnerJoin` dlg `InnerJoin` tx `InnerJoin` blk) -> do
+            on (blk ^. BlockId ==. tx ^. TxBlock)
+            on (dlg ^. DelegationTxId ==. tx ^. TxId)
             on (saddr ^. StakeAddressId ==. dlg ^. DelegationAddrId)
             where_ (saddr ^. StakeAddressHashRaw ==. val addr)
             where_ (dlg ^. DelegationActiveEpochNo <=. val epoch)
-            orderBy [desc (dlg ^. DelegationActiveEpochNo)]
+            -- Need to order by BlockSlotNo descending for correct behavior when there are two
+            -- or more delegation certificates in a single epoch.
+            orderBy [desc (blk ^. BlockSlotNo)]
             pure (saddr ^. StakeAddressId, dlg ^. DelegationPoolHashId)
     maybe queryPool (pure . Right . unValue2) (listToMaybe res)
   where
     queryPool :: MonadIO m => ReaderT SqlBackend m (Either LookupFail (StakeAddressId, PoolHashId))
     queryPool = do
-      res <- select . from $ \ (saddr `InnerJoin` pu) -> do
+      res <- select . from $ \ (saddr `InnerJoin` pu `InnerJoin` tx `InnerJoin` blk) -> do
+                on (blk ^. BlockId ==. tx ^. TxBlock)
+                on (pu ^. PoolUpdateRegisteredTxId ==. tx ^. TxId)
                 on (saddr ^. StakeAddressId ==. pu ^. PoolUpdateRewardAddrId)
                 where_ (saddr ^. StakeAddressHashRaw ==. val addr)
                 where_ (pu ^. PoolUpdateActiveEpochNo <=. val epoch)
-                orderBy [desc (pu ^. PoolUpdateActiveEpochNo)]
+                -- Need to order by BlockSlotNo descending for correct behavior when there are two
+                -- or more pool update certificates in a single epoch.
+                orderBy [desc (blk ^. BlockSlotNo)]
                 pure (saddr ^. StakeAddressId, pu ^. PoolUpdateHashId)
       pure $ maybeToEither (DbLookupMessage $ "StakeAddressAndPool " <> renderByteArray addr) unValue2 (listToMaybe res)
 
@@ -112,6 +120,9 @@ queryStakeAddressRef addr =
                 where_ (blk ^. BlockSlotNo ==. just (val slot))
                 where_ (tx ^. TxBlockIndex ==. val (fromIntegral txIx))
                 where_ (dlg ^. DelegationCertIndex ==. val (fromIntegral certIx))
+                -- Need to order by BlockSlotNo descending for correct behavior when there are two
+                -- or more delegation certificates in a single epoch.
+                orderBy [desc (blk ^. BlockSlotNo)]
                 pure (dlg ^. DelegationAddrId)
       pure $ unValue <$> listToMaybe res