如何从两个不同的，不相关的表中获取最新的行，并将它们合并到一个结果集中？

Question

I have two different tables with their schema given below:

Table1:

COLUMN_NAME     COLUMN_TYPE

campaign_id     varchar(50)
subscriber_id   varchar(50)
message         varchar(21000)
log_time        datetime
log_type        varchar(50)
level           varchar(50)
campaign_name   varchar(500)

Table2:

COLUMN_NAME      COLUMN_TYPE

guid             varchar(100)
sid              varchar(100)
url              varchar(2500)
ip               varchar(20)
is_new           varchar(20)
ref              varchar(2500)
user_agent       varchar(255)
stats_time       datetime
country          varchar(50)
region           varchar(50)
city             varchar(50)
city_lat_long    varchar(50)
email            varchar(100)

I need a table which is a merge of these two tables(not all the columns) and the rows should sorted based on time (which is log_time in Table1 and stats_time in Table2). There is no relation between these two tables.

The columns which I need from Table1 are

campaign_id
subscriber_id
message
log_time
log_type
campaign_name

and the columns which I need from Table2 are:

url
stats_time
email

Can I get more optimised solution?

Query:

SELECT url, ip, stats_time, email, campaign_id, subscriber_id, campaign_name, log_time, log_type, time from
(  
( SELECT url,ip,stats_time,email,NULL AS campaign_id,NULL AS subscriber_id ,NULL AS campaign_name,NULL AS log_time,NULL AS log_type, NULL AS message, UNIX_TIMESTAMP(stats_time) AS time FROM Tabel2 AS Table2Alias WHERE URL !='' AND EMAIL != '') Order by stats_time desc Limit 100

UNION ALL  

( SELECT NULL AS url,NULL AS ip,NULL AS stats_time,NULL AS email,campaign_id,subscriber_id,campaign_name,log_time,log_type,message,UNIX_TIMESTAMP(log_time) AS time FROM Table1 AS Table1Alias WHERE (log_type='x1' OR log_type='x2' OR log_type='x3' OR log_type='x4') order by log_time desc Limit 100)
)
as ResultTable order by time  desc

Answer 1

Select the top Limit + Offset records from each table, UNION the results, then select from the UNION.

So if user is viewing page 5, and there are 20 items per page, you will be selecting top 100 from each table, performing UNION, then selecting 20 records from result.

Answer 2

Some pseudocode for you -

 SELECT 
     /* columns you want */ 
 FROM 
     (
         SELECT 
             /* columns you want */
         FROM
             /* Table1 */ 
         ORDER BY 
             /* Date DESC */
         LIMIT 20 

         UNION ALL 

         SELECT 
             /* columns you want */
         FROM
             /* Table2 */ 
         ORDER BY 
             /* Date DESC */
         LIMIT 20 
    ) 
ORDER BY 
     /* Date DESC */
LIMIT 20