diff --git a/src/db/_private/Tselect.php b/src/db/_private/Tselect.php
index 5f70171..a8304aa 100644
--- a/src/db/_private/Tselect.php
+++ b/src/db/_private/Tselect.php
@@ -10,6 +10,12 @@ trait Tselect {
     return preg_match("/^select\b/i", $sql);
   }
 
+  private static function add_prefix(string $col, ?string $prefix): string {
+    if ($prefix === null) return $col;
+    if (strpos($col, ".") !== false) return $col;
+    return "$prefix$col";
+  }
+
   /**
    * parser une chaine de la forme
    * "select [COLS] [from TABLE] [where CONDS] [order by ORDERS] [group by GROUPS] [having CONDS]"
@@ -44,10 +50,10 @@ trait Tselect {
         if ($key === $index) {
           $index++;
           $cols[] = $col;
-          $usercols[] = "${colPrefix}$col";
+          $usercols[] = self::add_prefix($col, $colPrefix);
         } else {
           $cols[] = $key;
-          $usercols[] = "${colPrefix}$col as $key";
+          $usercols[] = self::add_prefix($col, $colPrefix)." as $key";
         }
       }
     } else {
@@ -55,11 +61,11 @@ trait Tselect {
       if ($schema && is_array($schema) && !in_array("*", $usercols)) {
         $cols = array_keys($schema);
         foreach ($cols as $col) {
-          $usercols[] = "${colPrefix}$col";
+          $usercols[] = self::add_prefix($col, $colPrefix);
         }
       }
     }
-    if (!$usercols && !$cols) $usercols = ["${colPrefix}*"];
+    if (!$usercols && !$cols) $usercols = [self::add_prefix("*", $colPrefix)];
     $sql[] = implode(", ", $usercols);
 
     ## from