add alter table variations:

set default
  drop default
  set not null
  drop not null
  set data type
  drop column
  add constraint
  drop constraint

fix bug where generated didn't have to be followed with 'always' or
  'by default' for identities in create table

Language/SQL/SimpleSQL/Syntax.lhs

@@ -553,13 +553,18 @@ I'm not sure if this is valid syntax or not.
 
 > data AlterTableAction =
 >     AddColumnDef ColumnDef
->   {-
->   | AlterColumnDef
->   | DropColumnDef
->   | AddTableConstraintDef
->   | AlterTableConstraintDef
->   | DropTableConstraintDef
->   -}
+>   | AlterColumnSetDefault Name ValueExpr
+>   | AlterColumnDropDefault Name
+>   | AlterColumnSetNotNull Name
+>   | AlterColumnDropNotNull Name
+>   | AlterColumnSetDataType Name TypeName
+>   {-  | AlterColumnAlterIdentity
+>   | AlterColumnDropIdentity
+>   | AlterColumnDropColumnGeneration-}
+>   | DropColumn Name DropBehaviour
+>   | AddTableConstraintDef (Maybe [Name]) TableConstraint
+>   --  | AlterTableConstraintDef
+>   | DropTableConstraintDef [Name] DropBehaviour
 >     deriving (Eq,Show,Read,Data,Typeable)
 
 > {-data ConstraintCharacteristics =
@@ -597,8 +602,7 @@ I'm not sure if this is valid syntax or not.
 >     deriving (Eq,Show,Read,Data,Typeable)
 
 > data IdentityWhen =
->     GeneratedDefault
->   | GeneratedAlways
+>     GeneratedAlways
 >   | GeneratedByDefault
 >     deriving (Eq,Show,Read,Data,Typeable)