> module Database.HsSqlPpp.Tests.TypeChecking.Joins
>     (tcJoinsTestData) where
>
> import Database.HsSqlPpp.Tests.TypeChecking.Utils

> import Database.HsSqlPpp.Types

> tcJoinsTestData :: Item
> tcJoinsTestData =
>     Group "simple join selects" [
>       s "select * from (select 1 as a, 2 as b) a\n\
>         \  cross join (select true as c, 4.5 as d) b;"
>         $ Right [Just ([], [("a", typeInt)
>                            ,("b", typeInt)
>                            ,("c", typeBool)
>                            ,("d", typeNumeric)])]
>      ,s "select * from (select 1 as a, 2 as b) a\n\
>         \  inner join (select true as c, 4.5 as d) b on true;"
>         $ Right [Just ([], [("a", typeInt)
>                            ,("b", typeInt)
>                            ,("c", typeBool)
>                            ,("d", typeNumeric)])]
>      ,s "select * from (select 1 as a, 2 as b) a\n\
>         \  inner join (select 1 as a, 4.5 as d) b using(a);"
>         $ Right [Just ([], [("a", typeInt)
>                            ,("b", typeInt)
>                            ,("d", typeNumeric)])]
>      ,s "select * from (select 1 as a, 2 as b) a\n\
>         \ natural inner join (select 1 as a, 4.5 as d) b;"
>         $ Right [Just ([], [("a", typeInt)
>                            ,("b", typeInt)
>                            ,("d", typeNumeric)])]
>         --check the attribute order
>      ,s "select * from (select 2 as b, 1 as a) a\n\
>         \ natural inner join (select 4.5 as d, 1 as a) b;"
>         $ Right [Just ([], [("a", typeInt)
>                            ,("b", typeInt)
>                            ,("d", typeNumeric)])]
>       --fixme: result set compatilibity check
>      {-,s "select * from (select 1 as a1, 2 as b) a\n\
>         \ natural inner join (select true as a1, 4.5 as d) b;"
>         $ Left [UnrecognisedCorrelationName ""
>                ,IncompatibleTypeSet [ScalarType "int4"
>                                     ,ScalarType "bool"]]-}
>       --fixme: result set compatilibity check
>       {-,s "select * from (select 1 as a1, 2 as b) a\n\
>         \ natural inner join (select true as a1, 4.5 as d) b;"
>         $ Left [UnrecognisedCorrelationName ""
>                ,IncompatibleTypeSet [ScalarType "int4"
>                                     ,ScalarType "bool"]]-}
>        ,s "select * from (select 1 as a1) a, (select 2 as a2) b;"
>         $ Right [Just ([], [("a1", typeInt)
>                                            ,("a2", typeInt)])]
>
>        ,s "select * from (select 1 as a1) a, (select 2 as a1) b;"
>         $ Right [Just ([], [("a1", typeInt)
>                                            ,("a1", typeInt)])]
>        --fixme: error detection (fixupids?)
>        {-,s "select a1 from (select 1 as a1) a,  (select 2 as a1) b;"
>         $ Left [AmbiguousIdentifier "a1"]-}
>      ]

>  where
>    s = StmtType