カーソルを使用して正しい方向に向けることができるかどうかを見てみましょう：
delimiter $$
create procedure findClosestTimeStamp()
begin
-- Variables to hold values from the communications table
declare cFromId int;
declare cTimeStamp datetime;
-- Variables related to cursor:
-- 1. 'done' will be used to check if all the rows in the cursor
-- have been read
-- 2. 'curComm' will be the cursor: it will fetch each row
-- 3. The 'continue' handler will update the 'done' variable
declare done int default false;
declare curComm cursor for
select fromId, timestamp from communication; -- This is the query used by the cursor.
declare continue handler for not found -- This handler will be executed if no row is found in the cursor (for example, if all rows have been read).
set done = true;
-- Open the cursor: This will put the cursor on the first row of its
-- rowset.
open curComm;
-- Begin the loop (that 'loop_comm' is a label for the loop)
loop_comm: loop
-- When you fetch a row from the cursor, the data from the current
-- row is read into the variables, and the cursor advances to the
-- next row. If there's no next row, the 'continue handler for not found'
-- will set the 'done' variable to 'TRUE'
fetch curComm into cFromId, cTimeStamp;
-- Exit the loop if you're done
if done then
leave loop_comm;
end if;
-- Execute your desired query.
-- As an example, I'm putting a SELECT statement, but it may be
-- anything.
select *
from movement as m
where m.vID = cFromId and m.timeStamp <= cTimeStamp
order by timestampdiff(SECOND, cTimeStamp, m.timeStamp)
limit 1;
end loop;
-- Don't forget to close the cursor when you finish
close curComm;
end $$
delimiter ;
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