在这种情况下，你可以使用LEFT JOIN和COALESCE。下面是示例代码：

SELECT 
    t1.id,
    t1.time AS conn,
    COALESCE(t1_disconn.time, t2.time) AS disconn
FROM table1 t1
LEFT JOIN table1 t1_disconn ON t1.id = t1_disconn.id AND t1_disconn.status = 'disconn'
LEFT JOIN table2 t2 ON t1.id = t2.id
WHERE t1.status = 'conn'
ORDER BY t1.id;

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下面是示例输出：

的数据
这里是fiddle link

或者，您也可以使用GROUP BY而不使用self join，如下所示：

SELECT
    T1.ID,
    MAX(CASE WHEN T1.STATUS = 'conn' THEN T1.TIME END) AS CONN,
    COALESCE(MAX(CASE WHEN T1.STATUS = 'disconn' THEN T1.TIME END), T2.TIME) AS DISCONN
  FROM
    table1 T1
      LEFT JOIN table2 T2 ON T1.ID = T2.ID
 GROUP BY T1.ID, T2.TIME
 ORDER BY T1.ID;

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