Fixes #6571 (#6578)

lib/impure/db_postgres.nim

@@ -98,15 +98,18 @@ proc dbFormat(formatstr: SqlQuery, args: varargs[string]): string =
   var a = 0
   if args.len > 0 and not string(formatstr).contains("?"):
     dbError("""parameter substitution expects "?" """)
-  for c in items(string(formatstr)):
-    if c == '?':
-      if args[a] == nil:
-        add(result, "NULL")
+  if args.len == 0:
+    return string(formatstr)
+  else:
+    for c in items(string(formatstr)):
+      if c == '?':
+        if args[a] == nil:
+          add(result, "NULL")
+        else:
+          add(result, dbQuote(args[a]))
+        inc(a)
       else:
-        add(result, dbQuote(args[a]))
-      inc(a)
-    else:
-      add(result, c)
+        add(result, c)
 
 proc tryExec*(db: DbConn, query: SqlQuery,
               args: varargs[string, `$`]): bool {.tags: [ReadDbEffect, WriteDbEffect].} =

tests/untestable/tpostgres.nim

@@ -304,7 +304,24 @@ doAssert parseInt(dbCols[40].typ.name) > 0
 doAssert dbCols[41].name == "range_col"
 doAssert dbCols[41].typ.kind == DbTypeKind.dbComposite
 doAssert dbCols[41].typ.name == "int4range"
-    
+
+# issue 6571
+db.exec(sql"DROP TABLE IF EXISTS DICTIONARY")
+db.exec(sql("""CREATE TABLE DICTIONARY(
+               id             SERIAL PRIMARY KEY,
+               entry      VARCHAR(1000) NOT NULL,
+               definition VARCHAR(4000) NOT NULL
+            );"""))
+var entry = "あっそ"
+var definition = "(int) (See ああそうそう) oh, really (uninterested)/oh yeah?/hmmmmm"
+discard db.getRow(
+  SqlQuery("INSERT INTO DICTIONARY(entry, definition) VALUES(\'$1\', \'$2\') RETURNING id" % [entry, definition]))
+doAssert db.getValue(sql"SELECT definition FROM DICTIONARY WHERE entry = ?", entry) == definition
+entry = "Format string entry"
+definition = "Format string definition"
+db.exec(sql"INSERT INTO DICTIONARY(entry, definition) VALUES (?, ?)", entry, definition)
+doAssert db.getValue(sql"SELECT definition FROM DICTIONARY WHERE entry = ?", entry) == definition
+
 echo("All tests succeeded!")
 
 db.close()