Sub queries for is_in and not_in

piccolo/columns/base.py

@@ -36,6 +36,7 @@
 
 if t.TYPE_CHECKING:  # pragma: no cover
     from piccolo.columns.column_types import ForeignKey
+    from piccolo.query.methods.select import Select
     from piccolo.table import Table
 
 
@@ -595,11 +596,21 @@ def _validate_choices(
 
         return True
 
-    def is_in(self, values: t.List[t.Any]) -> Where:
-        if len(values) == 0:
-            raise ValueError(
-                "The `values` list argument must contain at least one value."
-            )
+    def is_in(self, values: t.Union[Select, t.List[t.Any]]) -> Where:
+        from piccolo.query.methods.select import Select
+
+        if isinstance(values, list):
+            if len(values) == 0:
+                raise ValueError(
+                    "The `values` list argument must contain at least one "
+                    "value."
+                )
+        elif isinstance(values, Select):
+            if len(values.columns_delegate.selected_columns) != 1:
+                raise ValueError(
+                    "A sub select must only return a single column."
+                )
+
         return Where(column=self, values=values, operator=In)
 
     def not_in(self, values: t.List[t.Any]) -> Where:

piccolo/columns/combination.py

@@ -13,6 +13,7 @@
 
 if t.TYPE_CHECKING:
     from piccolo.columns.base import Column
+    from piccolo.query.methods.select import Select
 
 
 class CombinableMixin(object):
@@ -146,18 +147,22 @@ def __init__(
         self,
         column: Column,
         value: t.Any = UNDEFINED,
-        values: t.Union[Iterable, Undefined] = UNDEFINED,
+        values: t.Union[Iterable, Undefined, Select] = UNDEFINED,
         operator: t.Type[ComparisonOperator] = ComparisonOperator,
     ) -> None:
         """
         We use the UNDEFINED value to show the value was deliberately
         omitted, vs None, which is a valid value for a where clause.
         """
+        from piccolo.query.methods.select import Select
+
         self.column = column
 
         self.value = value if value == UNDEFINED else self.clean_value(value)
         if values == UNDEFINED:
             self.values = values
+        elif isinstance(values, Select):
+            self.values = values
         else:
             self.values = [self.clean_value(i) for i in values]  # type: ignore
 
@@ -190,11 +195,16 @@ def clean_value(self, value: t.Any) -> t.Any:
 
     @property
     def values_querystring(self) -> QueryString:
+        from piccolo.query.methods.select import Select
+
         values = self.values
 
         if isinstance(values, Undefined):
             raise ValueError("values is undefined")
 
+        if isinstance(values, Select):
+            return values.querystrings[0]
+
         template = ", ".join("{}" for _ in values)
         return QueryString(template, *values)