db: Unify SQL types of epoch_stake.epoch_no and epoch.no

These need to be the same SQL types for the Hasura code generation.
The fact that they were not the same type was a mistake.

Closes: #811

cardano-db/src/Cardano/Db/Schema.hs

@@ -311,7 +311,7 @@ share
     addrId              StakeAddressId      OnDeleteCascade
     poolId              PoolHashId          OnDeleteCascade
     amount              DbLovelace          sqltype=lovelace
-    epochNo             Word64
+    epochNo             Word64              sqltype=uinteger
     UniqueStake         epochNo addrId poolId
 
   Treasury

schema/migration-2-0024-20210913.sql

@@ -0,0 +1,20 @@
+-- Persistent generated migration.
+
+CREATE FUNCTION migrate() RETURNS void AS $$
+DECLARE
+  next_version int ;
+BEGIN
+  SELECT stage_two + 1 INTO next_version FROM schema_version ;
+  IF next_version = 24 THEN
+    EXECUTE 'ALTER TABLE "epoch_stake" ALTER COLUMN "epoch_no" TYPE uinteger' ;
+    EXECUTE 'ALTER TABLE "redeemer" ADD CONSTRAINT "redeemer_datum_id_fkey" FOREIGN KEY("datum_id") REFERENCES "datum"("id") ON DELETE CASCADE  ON UPDATE RESTRICT' ;
+    -- Hand written SQL statements can be added here.
+    UPDATE schema_version SET stage_two = next_version ;
+    RAISE NOTICE 'DB has been migrated to stage_two version %', next_version ;
+  END IF ;
+END ;
+$$ LANGUAGE plpgsql ;
+
+SELECT migrate() ;
+
+DROP FUNCTION migrate() ;