问题
TABLE:
**timeslot**:
----------
id_timeslot times
1 09:00
2 09:30
3 10:00
4 10:30
5 11:00
**bookslot**
id id_timeslot date b_ref
-------------------------------------------
1 2 2010-02-22 001
2 3 2010-02-22 001
3 4 2010-02-22 001
4 5 2010-02-22 001
5 2 2010-02-25 002
6 3 2010-02-27 003
7 4 2010-02-27 003
8 5 2010-02-27 003
PHP
$q = $mysqli->query("SELECT * FROM bookslot
LEFT JOIN timeslot ON bookslot.id_timeslot = timeslot.id_timeslot
WHERE bookslot.status = 1
GROUP BY bookslot.b_ref
ORDER BY bookslot.date ASC, bookslot.id_timeslot ASC LIMIT 20");
HTML RESULT:
DATE TIMES
2010-02-22 10:30
2010-02-25 09:30
2010-02-27 11:00
anyone notice that on the table result. the times is incorrect order?
i changed another way round with ASC / DESC, and still the times showing the last id_timeslot?
EXPECTED RESULT:
DATE TIMES
2010-02-22 09:30
2010-02-25 09:30
2010-02-27 10:00
回答1:
Your GROUP BY bookslot.b_ref is grouping the records, so you're only seeing the last time in each case.
Try using
SELECT date, time, MIN(bookslot.id_timeslot)
FROM bookslot
LEFT JOIN timeslot ON bookslot.id_timeslot = timeslot.id_timeslot
WHERE bookslot.status = 1
GROUP BY bookslot.b_ref
ORDER BY bookslot.date ASC, bookslot.id_timeslot ASC LIMIT 20
回答2:
While your SQL is syntactically correct but it will produce unexpected results.
Normally, the columns that you SELECT must be specified in the GROUP BY clause or should be enclosed inside an aggregate function. Otherwise, MySQL will determine, at its own discretion, which records to eliminate in the GROUP BY operation. The ORDER BY does not matter because it is applied after the GROUP BY operation. You should better revise your query like this:
SELECT b_ref, MIN(ADDTIME(date, times)) AS complete_datetime
FROM bookslot
LEFT JOIN timeslot ON bookslot.id_timeslot = timeslot.id_timeslot
WHERE bookslot.status = 1
GROUP BY bookslot.b_ref
ORDER BY bookslot.date, bookslot.id_timeslot
回答3:
Since the goal appears to be about collecting the earliest timeslots for each bookslot then it's required to narrow the results with MIN
SELECT b.id, b.id_timeslot, b.date, MIN(`date`) , t.times
FROM bookslot b
LEFT JOIN timeslot t ON b.id_timeslot = t.id_timeslot
GROUP BY b.b_ref
来源：https://stackoverflow.com/questions/5078381/php-mysql-asc-desc-order