feat: add foreign key support

example.json

@@ -1,16 +1,4 @@
 [
-  {
-    "name": "products",
-    "strict": false,
-    "columns": [
-      {
-        "name": "id",
-        "datatype": "Integer",
-        "primary_key": true,
-        "auto_increment": true
-      }
-    ]
-  },
   {
     "name": "users",
     "strict": true,
@@ -22,18 +10,68 @@
         "auto_increment": true
       },
       {
-        "name": "name",
+        "name": "username",
         "datatype": "Text",
-        "unique": true
-      },
-      {
-        "name": "password",
-        "datatype": "Text"
+        "unique": true,
+        "nullable": false
       },
       {
         "name": "email",
         "datatype": "Text",
-        "unique": true
+        "unique": true,
+        "nullable": false
+      },
+      {
+        "name": "password_hash",
+        "datatype": "Text",
+        "nullable": false
+      },
+      {
+        "name": "created_at",
+        "datatype": "Text",
+        "default": "CURRENT_TIMESTAMP",
+        "nullable": false
+      }
+    ]
+  },
+  {
+    "name": "posts",
+    "strict": true,
+    "columns": [
+      {
+        "name": "id",
+        "datatype": "Integer",
+        "primary_key": true,
+        "auto_increment": true
+      },
+      {
+        "name": "user_id",
+        "datatype": "Integer",
+        "nullable": false
+      },
+      {
+        "name": "title",
+        "datatype": "Text",
+        "nullable": false
+      },
+      {
+        "name": "content",
+        "datatype": "Text",
+        "nullable": false
+      },
+      {
+        "name": "created_at",
+        "datatype": "Text",
+        "default": "CURRENT_TIMESTAMP",
+        "nullable": false
+      }
+    ],
+    "foreign_keys": [
+      {
+        "name": "fk_posts_user",
+        "table_column_name": "user_id",
+        "other_table_name": "users",
+        "other_table_column_name": "id"
       }
     ]
   }