diff --git a/add-iban-mieter.sql b/add-iban-mieter.sql
deleted file mode 100644
index 880fd94..0000000
--- a/add-iban-mieter.sql
+++ /dev/null
@@ -1,2 +0,0 @@
-alter table mieter
-    add column iban varchar(34);
\ No newline at end of file
diff --git a/format-iban.sql b/format-iban.sql
index 87fae3f..26d1b31 100644
--- a/format-iban.sql
+++ b/format-iban.sql
@@ -1,3 +1,6 @@
+alter table mieter
+    add column iban varchar(34);
+
 delimiter //
 
 create or replace function format_iban(p_iban varchar(34)) returns varchar(34)
@@ -30,4 +33,32 @@ begin
 end;
 //
 
+create or replace function check_iban(p_iban varchar(34)) returns boolean
+begin
+    declare v_country varchar(2);
+    declare v_result boolean;
+    declare v_rearranged_iban varchar(36);
+    declare v_numeric_iban decimal(36, 0);
+    declare v_numeric_result decimal(36, 0);
+
+    set v_country = substring(p_iban from 1 for 2);
+
+    if (v_country = 'DE') then
+        set v_rearranged_iban = concat(substring(p_iban from 5), '1314', substring(p_iban from 3 for 2));
+        set v_numeric_iban = cast(v_rearranged_iban as decimal(36, 0));
+        set v_numeric_result = v_numeric_iban % 97;
+        if (v_numeric_result = 1) then
+            set v_result = TRUE;
+        else
+            set v_result = FALSE;
+        end if;
+    else
+        set v_result = TRUE;
+    end if;
+
+    return v_result;
+end;
+//
+
+
 delimiter ;