diff --git a/src/type/dynamicQueries.ts b/src/type/dynamicQueries.ts
index ca6a7e5..2d870b7 100644
--- a/src/type/dynamicQueries.ts
+++ b/src/type/dynamicQueries.ts
@@ -3,7 +3,7 @@ export interface DynamicQueryStructure {
   select: string[] | "*";
   table: string;
   where?: Array<ConditionStructure>;
-  join?: Array<DynamicQueryStructure & { foreignColumn: string }>;
+  join?: Array<DynamicQueryStructure & JoinStructure>;
   orderBy?: Array<OrderByStructure>; // only at top level
 }
 
@@ -48,6 +48,8 @@ export type WhereOperation =
   | "timespanEq"; // Date before x years (YYYY-01-01 <bis> YYYY-12-31)
 // TODO: age between | age equals | age greater | age smaller
 
+export type JoinStructure = { foreignColumn: string; type: "defined" } | { condition: string; type: "custom" };
+
 export type OrderByStructure = {
   id: string;
   depth: number;
@@ -101,18 +103,21 @@ export const exampleQuery: DynamicQueryStructure = {
       select: "*",
       table: "communication",
       foreignColumn: "sendNewsletter",
+      type: "defined",
     },
     {
       id: "91011",
       select: "*",
       table: "membership",
       foreignColumn: "memberships",
+      type: "defined",
       join: [
         {
           id: "121314",
           select: "*",
           table: "membership_status",
           foreignColumn: "status",
+          type: "defined",
           where: [
             {
               structureType: "condition",