Selecting more then one column when groupBy is present (db_select) - Drupal 8 added 'ONLY_FULL_GROUP_BY'
This is pretty annoying, but it is to provide cross database compatibility for Drupal.  You can get around it by adding the following to your database connection array if you only ever intend to live in MySQL compatible land:

'init_commands' =&gt; [
  'sql_mode' =&gt; "SET sql_mode = 'ANSI,STRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER'",
],


But I haven't yet figured out how to disable in my Kernel tests.  Still getting something like "PDOException: SQLSTATE[42000]: Syntax error or access violation: 1055 'local.nfd.title' isn't in GROUP BY"