Added test case for PR #695

beam-core/test/Database/Beam/Test/SQL.hs

@@ -12,7 +12,7 @@ import Database.Beam.Test.Schema hiding (tests)
 import Database.Beam
 import Database.Beam.Backend.SQL (MockSqlBackend)
 import Database.Beam.Backend.SQL.AST
-
+import Data.Kind (Type)
 import Data.Int
 import Data.Time.Clock
 import Data.Text (Text)
@@ -24,6 +24,7 @@ tests :: TestTree
 tests = testGroup "SQL generation tests"
                   [ simpleSelect
                   , simpleWhere
+                  , simpleWhereNoFrom
                   , simpleJoin
                   , selfJoin
                   , leftJoin
@@ -118,6 +119,32 @@ simpleWhere =
 
      selectWhere @?= Just (ExpressionBinOp "AND" salaryCond (ExpressionBinOp "AND" ageCond nameCond))
 
+-- | Simple select without FROM clause (#667)
+
+data EmptyDb (f :: Type -> Type) = EmptyDb
+
+simpleWhereNoFrom :: TestTree
+simpleWhereNoFrom =
+  testCase "WHERE clause not dropped if there is no FROM" $ do
+    SqlSelect Select { selectTable = SelectTable { .. }, .. } <- pure $ selectMock simple
+
+    selectGrouping @?= Nothing
+    selectOrdering @?= []
+    selectLimit @?= Nothing
+    selectOffset @?= Nothing
+    selectHaving @?= Nothing
+    selectQuantifier @?= Nothing
+    -- Important point: no FROM clause, yet WHERE clause should still be here
+    selectFrom @?= Nothing
+    selectWhere @?= (Just (ExpressionValue (Value False)))
+
+  where
+    simple :: Q (MockSqlBackend Command) EmptyDb s (QExpr (MockSqlBackend Command) s Bool)
+    simple = do
+      guard_ (val_ False)
+      pure (val_ True)
+
+
 -- | Ensure that multiple tables are correctly joined
 
 simpleJoin :: TestTree