mermaid: correction

banque.md

@@ -172,14 +172,21 @@ erDiagram
     text code PK
   }
 
+  exchange_rate {
+    date date PK
+    text currency_code PK/FK
+    decimal rate
+  }
+
   %% Relations
 
-  person  ||--|| holder
+  person  ||--|| holder :
-  company ||--|| holder
+  company ||--|| holder :
-  bank    ||--|| holder
+  bank    ||--|| holder :
-  holder  }|--|{ account_holder
+  holder  }|--|{ account_holder :
-  account_holder }|--|{ account
+  account_holder }|--|{ account :
-
+  currency ||--|{ account :
+  exchange_rate }o--|| currency :
 ```
 
 ## 4. Procédure stockée