mysql - SQL 从不同的表中获取值

Question

我有 2 个 sql 表，例如：

user_logs 
-id
-log_date
-log

system_logs
-id
-create_date
-log

是否可以从这些表中获取值并按日期对它们进行排序？

Answer 1

您是否正在寻找类似此查询的内容

(select id, date, log from user_logs)
union
(select id, date, log from system_logs)
order by date;

更好的设计可能是使用一个包含 id、date、log 和 log_type 列的表，其中 log_type 定义日志是用户日志还是系统日志。

Answer 2

SELECT id, date FROM user_logs UNION SELECT id, date from system_logs ORDER BY date DESC;

或类似的东西，无论如何 UNION 是您正在寻找的关键字，请参阅链接。

Answer 3

尝试使用UNION

SELECT *
FROM
(
    SELECT id, date, log FROM user_logs
    UNION
    SELECT id, date, log FROM system_logs
)
ORDER BY date desc

Answer 4

   SELECT *
FROM
( SELECT id,
           date,
           log
    FROM system_logs

    UNION

    SELECT id,
           date,
           log
    FROM user_logs) order by date  DESC

或者

SELECT id,
               date,
               log
        FROM system_logs

        UNION

        SELECT id,
               date,
               log
        FROM user_logs order by date  DESC