Have found similar posts but still stuck - I am trying to apply a sort AFTER I have processed a query and limited the results. My code is
select DISTINCT(t.id) t_id, t.cart_id ,tS.id tS_id, tS.created tS_created, t.value, t.transactionType_id tT_id, tS.member_name, outIn, tT.type type
from(transaction t)
join transactionSummary tS ON tS.id = t.transactionSummary_id
left join transactionType tT ON tT.id = t.transactionType_id
order by t.id DESC
limit 50
I have tried doing a sub select and applying the ORDER BY afterwards but get an error saying Unknown column 't.id' in 'field list'.
The above code (ie without the sub select) works fine but the ORDER BY slows it down so much as the table is huge...
Any suggestions?
Since you're aliasing t.id to t_id, you need to use the alias in the outer query.
SELECT *
FROM (select DISTINCT t.id t_id, t.cart_id ,tS.id tS_id, tS.created tS_created, t.value, t.transactionType_id tT_id, tS.member_name, outIn, tT.type type
from transaction t
join transactionSummary tS ON tS.id = t.transactionSummary_id
left join transactionType tT ON tT.id = t.transactionType_id
limit 50) x
ORDER BY t_id DESC
BTW, the way you wrote DISTINCT(t.id) suggests that you think the distinct operation is only being applied to that one column. DISTINCT applies to the entire SELECT list; if you only want to make certain columns distinct, you must use GROUP BY to specify those columns.
Here's a possible way to rewrite the query that may make it faster:
select DISTINCT t.id t_id, t.cart_id ,tS.id tS_id, tS.created tS_created, t.value, t.transactionType_id tT_id, tS.member_name, outIn, tT.type type
from transaction t
join (select max(id)-500 maxid from transaction) mT on t.id > maxid
join transactionSummary tS ON tS.id = t.transactionSummary_id
left join transactionType tT ON tT.id = t.transactionType_id
order by t_id DESC
limit 50
By filtering down to just the top 500 IDs, the size of the joins and sorting are reduced.
Related
I am working with a query, which looks like this
SELECT s.c1, s.t, s.u, s.dt, t.temp, t.dt AS dt2
FROM `systemusage` AS s
INNER JOIN temperature AS t ON s.did=t.did
WHERE t.did = (SELECT id FROM devices WHERE m = 1)
LIMIT 1
Which works just fine, however if I add ORDER BY s.id, then the query gets totally stuck, can someone guide me on why? the id field is primary, so it should be indexed no?
Add an index on the column temperature.did so that the WHERE clause can be implemented efficiently.
It also may help to replace WHERE t.did = (SELECT ...) with a JOIN.
SELECT s.c1, s.t, s.u, t.temp
FROM `systemusage` AS s
INNER JOIN temperature AS t ON s.did=t.did
INNER JOIN devices AS d ON d.id = t.did
WHERE d.m = 1
ORDER BY s.id DESC, t.id DESC
LIMIT 1
I have the following query that is doing an INNER JOIN within a select query to insert records into the table. The issue is instead of using the WHERE clause and listing the 3 t2.device I would like to see, I need to do another INNER JOIN with a table called tbl_Full_List.
Both tbl_Full_List and tbl1_device have a column called device so instead of the WHERE clause I would like it to show only devices that match in both tbl_Full_List and tbl1_device
INSERT INTO TEMP_Table1 (place, device, description, quantity)
(SELECT t1.place, t2.device, t2.description, Sum(t2.quantity) AS quantity
FROM Device_Table AS t1
INNER JOIN tbl1_device AS t2
ON t1.rma = t2.rma
WHERE t2.device IN ('PRT1030', 'PRT-23','PRT-20139')
AND t1.date_made = Current_Date()
GROUP BY t1.place, t2.device, t2.description ORDER BY place ASC, device ASC )
Without knowing how the two relate... I'm assuming FL.ID is the PK of full list and we have a Foreign Key to tbl1_devcice called FL_ID
INSERT INTO TEMP_Table1 (place, device, description, quantity)
(SELECT t1.place, t2.device, t2.description, Sum(t2.quantity) AS quantity
FROM Device_Table AS t1
INNER JOIN tbl1_device AS t2
ON t1.rma = t2.rma
INNER JOIN tbl_Full_List FL
ON FL.Device = t2.Device
WHERE t1.date_made = Current_Date()
GROUP BY t1.place, t2.device, t2.description ORDER BY place ASC, device ASC )
Table:
Table
Help me in. I'm suck in SubQuery. I wanna get the latest Name from every category group
Output:
Output
I already search some reference in google and still didn't understand. Hopefully this time I can understand
you can use join on max_date for each category
select * from
my_table m
inner join (
select category, max(date) max_date
from my_table
group by category) as t on m.date = t.max_date and m.category = t.category
Thx scaisEdge!!
I finally got it!
So this is my final query
select m.id, m.category, m.name, m.time
from my_table m
inner join (
select id, category, name, time
from my_table
order by id desc
) as t
on m.id = t.id
group by category
In mysql query I use order by, but it is not working.
When I do this
SELECT t.id,t.user_id,t.title,c.comment,d.has_answer,IF(c.id IS NULL, t.date_created, d.recent_date) recent_date,MIN(i.id) image_id
FROM threads t
LEFT JOIN comments c ON c.thread_id = t.id
INNER JOIN (
SELECT thread_id, MAX(date_sent) recent_date, MAX(is_answer) has_answer
FROM comments
GROUP BY thread_id
) d ON c.id IS NULL OR (d.thread_id = c.thread_id AND d.recent_date = c.date_sent)
LEFT JOIN thread_images i ON t.id = i.thread_id
WHERE t.user_id = t.user_id
GROUP BY t.id
ORDER BY d.recent_date DESC
LIMIT 0, 10
It doesn't properly order them. But if I do this:
SELECT *
FROM (
SELECT t.id,t.user_id,t.title,c.comment,d.has_answer,IF(c.id IS NULL, t.date_created, d.recent_date) recent_date,MIN(i.id) image_id
FROM threads t
LEFT JOIN comments c ON c.thread_id = t.id
INNER JOIN (
SELECT thread_id, MAX(date_sent) recent_date, MAX(is_answer) has_answer
FROM comments
GROUP BY thread_id
) d ON c.id IS NULL OR (d.thread_id = c.thread_id AND d.recent_date = c.date_sent)
LEFT JOIN thread_images i ON t.id = i.thread_id
WHERE t.user_id = t.user_id
GROUP BY t.id
LIMIT 0, 10) qwerty
ORDER BY recent_date DESC
Then it does work. Why does the top one not work, and is the second way the best way to fix that?
Thanks
Those two statements are ordering by two different things.
The second statement is ordering by the result of an expression in the SELECT list.
But the first statement specifies ordering by a value of recent_date returned by the inline view d; if you remove "d." from in front of recent_date, then the ORDER BY clause would reference the alias assigned to the expression in the SELECT list, as the second statement does.
Because recent_date is an alias for an expression the SELECT list, these two are equivalent:
ORDER BY recent_date
ORDER BY IF(c.id IS NULL, t.date_created, d.recent_date)
^^
but those are significantly different from:
ORDER BY d.recent_date
^^
Note that the non-standard use of the GROUP BY clause may be masking some values of recent_date which are discarded by the query. This usage of the GROUP BY clause is a MySQL extension to the SQL Standard; most other relational databases would throw an error with this statement. It's possible to get MySQL to throw the same type of error by enabling the ONLY_FULL_GROUP_BY SQL mode.
Q Is the second statement the best way to fix that?
A If that statement guarantees that the resultset returned meets your specification, then it's a workable approach. (One downside is the overhead of the inline view query.)
But I strongly suspect that the second statement is really just masking the problem, not really fixing it.
SELECT t.id,t.user_id,t.title,c.comment,d.has_answer,IF(c.id IS NULL, t.date_created, d.recent_date) recent_date,MIN(i.id) image_id
FROM (threads t
LEFT JOIN comments c ON c.thread_id = t.id
INNER JOIN (
SELECT thread_id, MAX(date_sent) recent_date, MAX(is_answer) has_answer
FROM comments
GROUP BY thread_id
) d ON c.id IS NULL OR (d.thread_id = c.thread_id AND d.recent_date = c.date_sent)
LEFT JOIN thread_images i ON t.id = i.thread_id
WHERE t.user_id = t.user_id
GROUP BY t.id
LIMIT 0, 10) x
ORDER BY d.recent_date DESC
This is a query automatically generated by Taggable extension for Doctrine ORM.
SELECT t.id AS t__id, t.name AS t__name, COUNT(DISTINCT i.id) AS i__0,
(COUNT(DISTINCT i.id)) AS i__1
FROM taggable_tag t
LEFT JOIN cms__model__image_taggable_tag c ON (t.id = c.tag_id)
LEFT JOIN image i ON i.id = c.id
WHERE t.id IN
(SELECT doctrine_subquery_alias.id
FROM
(SELECT DISTINCT t2.id, (COUNT(DISTINCT i2.id)) AS i2__1
FROM taggable_tag t2
LEFT JOIN cms__model__image_taggable_tag c2 ON (t2.id = c2.tag_id)
LEFT JOIN image i2 ON i2.id = c2.id
GROUP BY t2.id HAVING i2__1 > 0
ORDER BY i2__1 DESC LIMIT 10) AS doctrine_subquery_alias)
GROUP BY t.id HAVING i__1 > 0
ORDER BY i__1 DESC
It works when using MySql, but won't work with PostgreSql.
I get: column i2__1 not found or column i__2 not found.
Are aliases disallowed when using COUNT(DISTINCT)?
How this query should look like to work on PostgreSql?
You could try to replace i2__1 by COUNT(DISTINCT i2.id) in the HAVING-clause of the sub-select, or remove the parenthesis around COUNT(DISTINCT i2.id).
You might also have to add t__name to the GROUP BY-clause of the main select.