noyearzero
msg:4467203 | 3:02 pm on Jun 19, 2012 (gmt 0) |
I'm not sure if this is exactly right....but it should put you on the path. (replace `tbl_access_log.id` with the actual primary index for the table `tbl_access_log`)
SELECT
tbl_access_log.fld_login,
tbl_access_log.fld_logout,
tbl_admin_user.*
FROM tbl_admin_users
LEFT JOIN tbl_access_log ON tbl_access_log.id = (
SELECT
tbl_access_log.id
FROM tbl_access_log
WHERE
tbl_access_log.fld_user_id = '" . $adminId . "'
ORDER BY
tbl_access_log.fld_logout DESC
LIMIT 1
)
Additionally, if your $adminId variable actually refers to the current row in the outer table (tbl_admin_users) you could replace
'" . $adminId . "'
with
tbl_admin_users.fld_user_id
(assuming fld_user_id is the name of the same field)
That would be more appropriate if your outer table is meant to pull back more than 1 row
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rocknbil
msg:4467246 | 4:20 pm on Jun 19, 2012 (gmt 0) |
I always get this wrong off the top of my head and have to mantra, it goes in this order:
select/from/join/where/order/limit
I'm guessing at a few of the field names.
$sql =
"select tbl_admin_users.username, tbl_access_log.login,tbl_access_log.logout
from tbl_admin_users
left join tbl_access_log on tbl_access_log.fld_user_id = tbl_admin_users.fld_user_id
where tbl_access_log.fld_user_id = '" . $adminId . "'
order by tbl_access_log.fld_logout desc limit 1";
Some notes:
- Do not use * unless you specifically need all fields, it's a lot of overhead that will cost you on complex multi table joins.
- If admin ID is numeric, which it should be, it doesn't need to be quoted (and shouldn't.)
where tbl_access_log.fld_user_id = $adminId
If it's just a single table select, and you're sure it always will be (i.e., no other potential joins in the near future) you can move the "joining" to the where clause:
$sql =
"select tbl_admin_users.username, tbl_access_log.login, tbl_access_log.logout
from tbl_admin_users,tbl_access_log
where tbl_access_log.fld_user_id = $adminId
and tbl_access_log.fld_user_id = tbl_admin_users.fld_user_id
order by tbl_access_log.fld_logout desc limit 1";
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neophyte
msg:4467418 | 12:27 am on Jun 20, 2012 (gmt 0) |
Noyearzero and Rockinbil -
Thanks to you both for your input on this - I was struggling for so long on this that I just settled for doing a multiple query routine that - while it works - is really inefficient. Now I can get back to doing it the right way.
Rockinbil - thanks also for the Mantra... I'm sure this will help others as well.
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noyearzero
msg:4468064 | 6:05 pm on Jun 21, 2012 (gmt 0) |
rocknbil:
Is there any speed advantage to 'move the "joining" to the where clause' as opposed to what i suggested? I always thought it was faster to filter out as many rows from the join table in the ON clause rather than in the FROM table's WHERE? But to be honest i could be completely wrong.
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rocknbil
msg:4468384 | 3:33 pm on Jun 22, 2012 (gmt 0) |
I don't know - bench test it. :-) My **guess** would be that your approach contains a nested select, and may traverse more rows because it's essentially two selects. The approach I suggested is certainly a little less complex in the coding part.
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