diff --git a/dds-backoffice/src/main/java/com/cloudhandson/ddsbackoffice/service/DdsQueryService.java b/dds-backoffice/src/main/java/com/cloudhandson/ddsbackoffice/service/DdsQueryService.java
index 869dabf..80c7a1d 100644
--- a/dds-backoffice/src/main/java/com/cloudhandson/ddsbackoffice/service/DdsQueryService.java
+++ b/dds-backoffice/src/main/java/com/cloudhandson/ddsbackoffice/service/DdsQueryService.java
@@ -85,7 +85,7 @@ public class DdsQueryService {
     var search = searchText == null ? "" : searchText.trim();
     var timeoutSeconds = timeoutSeconds(properties.queryTimeout());
     var connectionProperties = new Properties();
-    connectionProperties.setProperty("user", user.username());
+    connectionProperties.setProperty("user", jdbcUsername(user.username()));
     connectionProperties.setProperty("password", user.password());
     connectionProperties.setProperty("oracle.net.CONNECT_TIMEOUT", String.valueOf(timeoutSeconds * 1000));
     connectionProperties.setProperty("oracle.jdbc.ReadTimeout", String.valueOf(timeoutSeconds * 1000));
@@ -168,6 +168,19 @@ public class DdsQueryService {
     return normalized;
   }
 
+  private static String jdbcUsername(String username) {
+    var normalized = username == null ? "" : username.trim();
+    if (normalized.length() >= 2 && normalized.startsWith("\"") && normalized.endsWith("\"")) {
+      return normalized;
+    }
+    // The standalone SQL creates quoted lower-case END USER names. Oracle's
+    // JDBC driver uppercases an unquoted username, so preserve that identity.
+    if (!normalized.isEmpty() && normalized.equals(normalized.toLowerCase(Locale.ROOT))) {
+      return "\"" + normalized.replace("\"", "\"\"") + "\"";
+    }
+    return normalized;
+  }
+
   private static int timeoutSeconds(Duration duration) {
     return Math.max(1, (int) Math.ceil(duration.toMillis() / 1000.0));
   }