这是一个有点不清楚我你想达到什么目的，但我认为你正在寻找过滤器。
但是由于agent.agent_name是唯一一个未分组的列，因此必须按 that 进行分组：

SELECT agent.agent_name AS agent_name,
       COUNT(assigned.id_agent) AS itung,
       COUNT(ticket.id_agent) FILTER (WHERE ticket.id_status = 4) AS itung2
FROM agent
  LEFT JOIN assigned ON agent.id = assigned.id_agent
  LEFT JOIN ticket ON agent.id = ticket.id_agent
GROUP BY agent.agent_name;

查看您的查询，您显然在group by子句中缺少了ticket.id_status。
或
查询可以通过聚合函数进一步简化，以计算itung2的值，如下所示：

SELECT agent.agent_name AS agent_name,
    COUNT(assigned.id_agent) AS itung,
    COUNT(ticket.id_agent) AS itung2
FROM agent
LEFT JOIN assigned ON agent.id = assigned.id_agent
LEFT JOIN ticket ON agent.id = ticket.id_agent AND ticket.id_status = 4
GROUP BY agent.id, agent.agent_name;