select data based on multiple criteria (cloest value) - mysql

Question

I am using MySQL. I'm trying to build something and just can't find a solution to a problem.
I am selecting a value from the lookup table based on my table as shown in the below example.
Select Criteria:
my.id<>l.id AND my.route1=l.route1 AND my.route2=l.route2 AND my.utc=l.utc
where my.stime is closest or same as l.stime
ex) my.id=2's col should get the l.id=1, l.etime=7777 since my.id<>l.id and the rest are the same.
ex) my,id=5's col has options l.id=3, l.etime=9999 and l.id=4, l.etime=7979 since my.id<>l.id, my.route=l.route, my.utc=l.utc. Yet, since my.stime=2220 is closer to l.stime=2222 than l.stime=3333 , l.id=3, l.etime=9999 will be chosen.
ex) my,id=6's col example is to select either value if "closest" is the same.
ex) my,id=7's col example is to return NULL when the criteria is not met.
Table: lookup (l.)
id route1 route2 utc stime etime
---|--------|--------|-----|-------|------
1 11 22 111 1111 7777
2 11 22 111 1111 8888
3 22 33 222 2222 9999
4 22 33 222 3333 7979
5 22 33 222 3335 8989
Table: my (my.) | result
id route1 route2 utc stime | l.id l.etime
---|--------|--------|-----|------- |-------|----------|
2 11 22 111 1111 | 1 7777
5 22 33 222 2220 | 3 9999
6 22 33 222 3334 | 4or5 7979or8989
7 22 33 999 9999 | null null
A new table should be created where the result is appended to the last col of my.
Any help is appreciated. Thanks in advance.

Answer 1

This solution is a bit convoluted, but it's a starting point.
First, let's create an auxiliary table:
CREATE TEMP TABLE temp AS
SELECT m.id mid, l.id lid, ABS(l.stime-m.stime) timediff
FROM my m JOIN lookup l
WHERE m.route1 = l.route1 AND m.route2 = l.route2 AND
m.utc = l.utc AND m.id <> l.id;
From this table we can get the minimum timediff for each my.id:
SELECT mid, min(timediff) mtimediff FROM temp GROUP BY mid
Result:
mid mtimediff
---------- ----------
2 0
5 2
6 1
Now we can find which rows in lookup have this stime difference, and choose the smallest id:
SELECT t.mid mid, min(lid) lid
FROM temp t JOIN (
SELECT mid, min(timediff) mtimediff FROM temp GROUP BY mid
) mt ON t.mid = mt.mid AND t.timediff = mt.mtimediff
GROUP BY t.mid
This is the result:
mid lid
---------- ----------
2 1
5 3
6 4
And finally we use those ids to extract the data from the tables:
SELECT m.id, m.route1, m.route2, m.utc, m.stime, l.id, l.etime
FROM my m JOIN lookup l JOIN (
SELECT t.mid mid, min(lid) lid
FROM temp t JOIN (
SELECT mid, min(timediff) mtimediff FROM temp GROUP BY mid
) mt ON t.mid = mt.mid AND t.timediff = mt.mtimediff
GROUP BY t.mid
) ON m.id = mid AND l.id = lid;
Giving:
id route1 route2 utc stime id etime
---------- ---------- ---------- ---------- ---------- ---------- ----------
2 11 22 111 1111 1 7777
5 22 33 222 2220 3 9999
6 22 33 222 3334 4 7979