Fix selectNextGroup query for an empty job table

modules/scheduler/impl/src/main/scala/docspell/scheduler/impl/QJob.scala

@@ -135,7 +135,7 @@ object QJob {
       .trace(
         s"nextGroupQuery: $frag  (now=${now.toMillis}, pause=${initialPause.millis})"
       ) *>
-      groups.build.query[Ident].option
+      frag.query[Option[Ident]].unique
   }
 
   private def stuckTriggerValue(t: RJob.Table, initialPause: Duration, now: Timestamp) =

modules/scheduler/impl/src/test/scala/docspell/scheduler/impl/QJobTest.scala

@@ -12,6 +12,7 @@ import java.util.concurrent.atomic.AtomicLong
 import cats.syntax.all._
 
 import docspell.common._
+import docspell.store.qb.{Condition, DML}
 import docspell.store.records.{RJob, RJobGroupUse}
 import docspell.store.{DatabaseTest, Db}
 
@@ -42,6 +43,19 @@ class QJobTest extends DatabaseTest {
       None
     )
 
+  Db.all.toList.foreach { db =>
+    test(s"selectNextGroup on empty table ($db)") {
+      val store = createStore(db)
+      val nextGroup = for {
+        _ <- store.transact(RJobGroupUse.deleteAll)
+        _ <- store.transact(DML.delete(RJob.T, Condition.unit))
+        next <- store.transact(QJob.selectNextGroup(worker, nowTs, initialPause))
+      } yield next
+
+      nextGroup.assertEquals(None)
+    }
+  }
+
   Db.all.toList.foreach { db =>
     test(s"set group must insert or update ($db)") {
       val store = createStore(db)

modules/store/src/main/scala/docspell/store/qb/DML.scala

@@ -20,9 +20,11 @@ object DML extends DoobieMeta {
   def delete(table: TableDef, cond: Condition): ConnectionIO[Int] =
     deleteFragment(table, cond).update.run
 
-  def deleteFragment(table: TableDef, cond: Condition): Fragment =
-    fr"DELETE FROM" ++ FromExprBuilder.buildTable(table) ++ fr" WHERE" ++ ConditionBuilder
-      .build(cond)
+  def deleteFragment(table: TableDef, cond: Condition): Fragment = {
+    val delete = fr"DELETE FROM" ++ FromExprBuilder.buildTable(table)
+    if (cond == Condition.unit) delete
+    else delete ++ fr"WHERE" ++ ConditionBuilder.build(cond)
+  }
 
   def insert(table: TableDef, cols: Nel[Column[_]], values: Fragment): ConnectionIO[Int] =
     insertFragment(table, cols, List(values)).update.run