将MySQL查询转换为SQLite

Question

I got the following MySQL query which I need to convert to a SQLite query (to use in my android application)

select *
from msgsList
where (least(msg_from, msg_to), greatest(msg_from, msg_to), msg_time)       
in 
(
    select 
       least(msg_from, msg_to) as x, greatest(msg_from, msg_to) as y, 
       max(msg_time) as msg_time
    from msgsList 
    group by x, y
);

Answer 1

In SQLite, LEAST()/GREATEST() are just called MIN()/MAX().

SQLite does not support IN with tuples, but you can join the table to the subquery instead:

SELECT msgsList.*
FROM msgsList
JOIN (SELECT MIN(msg_from, msg_to) AS x,
             MAX(msg_from, msg_to) AS y,
             MAX(msg_time) AS msg_time
     FROM msgsList
     GROUP BY x, y) AS m
ON m.x        = MIN(msgsList.msg_from, msgsList.msg_to) AND
   m.y        = MAX(msgsList.msg_from, msgsList.msg_to) AND
   m.msg_time = msgsList.msg_time;

If you have SQLite 3.7.11 or later (which is not available in all Android versions ), you can simply use the aggregate MAX() to select the rows to return:

SELECT *,
       MAX(msg_time)
FROM msgsList
GROUP BY MIN(msg_from, msg_to),
         MAX(msg_from, msg_to);

Answer 2

您可以使用SQLiteDatabse类的rawQuery(String query)运行。