This is mostly a SQL syntax / SQL capability question. Why does the following query NOT work:
SELECT * from
(
select m.*, p.type,
from multipliers m
inner join pushes p
on m.push_id = p.id
where p.type = 'CONSTANT'
) AS res1 where res1.push_id = (
select max(push_id) from res1
);
when the following completes without issue:
SELECT * from
(
select m.*, p.type,
from multipliers m
inner join pushes p
on m.push_id = p.id
where p.type = 'CONSTANT'
) AS res1 where res1.push_id = (
select max(push_id) from
(
select m.push_id
from multipliers m
inner join pushes p
on m.push_id = p.id
where p.type = 'CONSTANT'
) AS res2
);
Per the MySQL 5.7 documentation:
Derived tables cannot be correlated subqueries, or contain outer references or references to other tables of the same SELECT.
In other words, you can't reference a derived table in a subquery. The documentation doesn't state this, but it likely acts this way because of an OOO issue since the derived table isn't necessarily processed before the subquery. In MySQL 8.0 you will be able to use a Common Table Expression or CTE, which basically lets you define a reusable derived table before your query, but until then use your second approach.
The first query doesn't work because the selected column doesn't exist. At least if you want to reuse it, it should be res.push_id, anyway it's better to use CTE as Jarlh said in his comment.
WITH
myCte AS ( select m.*, p.type,
from multipliers m
inner join pushes p
on m.push_id = p.id
where p.type = 'CONSTANT')
SELECT * FROM myCte
WHERE myCte.push_id = (SELECT MAX(push_id) FROM myCte)
The error in the 1st query is that a table alias (correlation name) can't be used as a table expression in a FROM.
A table alias with a dot & column identifies a column of a table. (In the predicate logic or relational calculus sense a table alias is a subrow-valued variable.)
Related
How can I merge these two left joins: http://sqlfiddle.com/#!9/1d2954/69/0
SELECT d.`id`, (adcount + bdcount)
FROM `docs` d
LEFT JOIN
(
SELECT da.`doc_id`, COUNT(da.`doc_id`) AS adcount FROM `docs_scod_a` da
INNER JOIN `scod_a` a ON a.`id` = da.`scod_a_id`
WHERE a.`ver_a` IN ('AA', 'AB')
GROUP BY da.`doc_id`
) ad ON ad.`doc_id` = d.`id`
LEFT JOIN
(
SELECT db.`doc_id`, COUNT(db.`doc_id`) AS bdcount FROM `docs_scod_b` db
INNER JOIN `scod_b` b ON b.`id` = db.`scod_b_id`
WHERE b.`ver_b` IN ('BA', 'BB')
GROUP BY db.`doc_id`
) bd ON bd.`doc_id` = d.`id`
to be a Single left join just to ease its use in my code, while making it no less slower?
Let me first emphasize that your method of doing the calculation is the better method. You have two separate dimensions and aggregating them separately is often the most efficient method for doing the calculation. It is also the most scalable method.
That said, your query should be equivalent to this version:
SELECT d.id,
count(distinct a.id),
count(distinct b.id)
FROM docs d left join
docs_scod_a da
ON da.doc_id = d.id LEFT JOIN
scod_a a
ON a.id = da.scod_a_id AND a.ver_a IN ('AA', 'AB') LEFT JOIN
docs_scod_b db
ON db.doc_id = d.id LEFT JOIN
scod_b b
ON b.id = db.scod_b_id AND b.ver_b IN ('BA', 'BB')
GROUP BY d.id
ORDER BY d.id;
This query is more expensive than it looks, because the COUNT(DISTINCT) incurs additional overhead compared to COUNT().
And here is the SQL Fiddle.
And, because LEFT JOIN can return NULL values, your query is more correctly written as:
SELECT d.`id`, COALESCE(adcount, 0) + COALESCE(bdcount, 0)
If you were having problems with the results, this small change might fix those problems.
Performance may be a big problem, depending on sizes of each table. It appears to be an "inflate-deflate" situation since it first "inflates" the number of rows via JOIN, then "deflates" via GROUP BY. The formulation below avoids inflation-deflation.
But first, if I understand this subquery correctly, this
SELECT da.`doc_id`, COUNT(da.`doc_id`) AS adcount
FROM `docs_scod_a` da
INNER JOIN `scod_a` a ON a.`id` = da.`scod_a_id`
WHERE a.`ver_a` IN ('AA', 'AB')
GROUP BY da.`doc_id`
can be rewritten as
SELECT `doc_id`,
( SELECT COUNT(*)
FROM `scod_a`
WHERE `id` = da.`scod_a_id`
AND `ver_a` IN ('AA', 'AB')
) AS adcount
FROM `docs_scod_a` AS da
If that is correct, then the entire query becomes
SELECT d.id,
( SELECT COUNT(*)
FROM docs_scod_a ds
JOIN scod_a s ON s.id = ds.scod_a_id
WHERE ds.doc_id = d.id
AND s.ver_a IN ('AA', 'AB')
) +
( SELECT COUNT(*)
FROM docs_scod_b ds
JOIN scod_b s ON s.id = ds.scod_b_id
WHERE ds.doc_id = d.id
AND s.ver_b IN ('BA', 'BB')
)
FROM docs AS d
Which needs these indexes:
docs_scod_a: (doc_id, scod_a_id), (scod_a_id, doc_id)
docs_scod_b: (doc_id, scod_b_id), (scod_b_id, doc_id)
scod_a: (ver_a, id)
scod_b: (ver_b, id)
docs: -- presumably has PRIMARY KEY(id)
Note the lack of GROUP BY.
docs_scod_a smells like a many-to-many mapping table. I recommend you follow the tips here.
(No COALESCE is needed since COUNT will simply return zero.)
(I don't know whether my version is better (faster or whatever) than Gordon's, nor whether my indexes will help his formulation.)
While working with following query on mysql, Its getting locked,
SELECT event_list.*
FROM event_list
INNER JOIN members
ON members.profilenam=event_list.even_loc
WHERE (even_own IN (SELECT frd_id
FROM network
WHERE mem_id='911'
GROUP BY frd_id)
OR even_own = '911' )
AND event_list.even_active = 'y'
GROUP BY event_list.even_id
ORDER BY event_list.even_stat ASC
The Inner query inside IN constraint has many frd_id, So because of that above query is slooow..., So please help.
Thanks.
Try this:
SELECT el.*
FROM event_list el
INNER JOIN members m ON m.profilenam = el.even_loc
WHERE el.even_active = 'y' AND
(el.even_own = 911 OR EXISTS (SELECT 1 FROM network n WHERE n.mem_id=911 AND n.frd_id = el.even_own))
GROUP BY el.even_id
ORDER BY el.even_stat ASC
You don't need the GROUP BY on the inner query, that will be making the database engine do a lot of unneeded work.
If you put even_own = '911' before the select from network, then if even_own IS 911 then it will not have to do the subquery.
Also why do you have a group by on the subquery?
Also run explain plan top find out what is taking the time.
This might work better:
( SELECT e.*
FROM event_list AS e
INNER JOIN members AS m ON m.profilenam = e.even_loc
JOIN network AS n ON e.even_own = n.frd_id
WHERE n.mem_id = '911'
AND e.even_active = 'y'
ORDER BY e.even_stat ASC )
UNION DISTINCT
( SELECT e.*
FROM event_list AS e
INNER JOIN members AS m ON m.profilenam = e.even_loc
WHERE e.even_own = '911'
AND e.even_active = 'y' )
ORDER BY e.even_stat ASC
Since I don't know whether the JOINs one-to-many (or what), I threw in DISTINCT to avoid dups. There may be a better way, or it may be unnecessary (that is, UNION ALL).
Notice how I avoid two things that are performance killers:
OR -- turned into UNION
IN (SELECT...) -- turned into JOIN.
I made aliases to cut down on the clutter. I moved the ORDER BY outside the UNION (and added parens to make it work right).
Everything in the following query results in one line for each invBlueprintTypes row with the correct information. But I'm trying to add something to it. See below the codeblock.
Select
blueprintType.typeID,
blueprintType.typeName Blueprint,
productType.typeID,
productType.typeName Item,
productType.portionSize,
blueprintType.basePrice * 0.9 As bpoPrice,
productGroup.groupName ItemGroup,
productCategory.categoryName ItemCategory,
blueprints.productionTime,
blueprints.techLevel,
blueprints.researchProductivityTime,
blueprints.researchMaterialTime,
blueprints.researchCopyTime,
blueprints.researchTechTime,
blueprints.productivityModifier,
blueprints.materialModifier,
blueprints.wasteFactor,
blueprints.maxProductionLimit,
blueprints.blueprintTypeID
From
invBlueprintTypes As blueprints
Inner Join invTypes As blueprintType On blueprints.blueprintTypeID = blueprintType.typeID
Inner Join invTypes As productType On blueprints.productTypeID = productType.typeID
Inner Join invGroups As productGroup On productType.groupID = productGroup.groupID
Inner Join invCategories As productCategory On productGroup.categoryID = productCategory.categoryID
Where
blueprints.techLevel = 1 And
blueprintType.published = 1 And
productType.marketGroupID Is Not Null And
blueprintType.basePrice > 0
So what I need to get in here is the following table with the columns below it so I can use the values timestamp and sort the entire result by profitHour
tablename: invBlueprintTypesPrices
columns: blueprintTypeID, timestamp, profitHour
I need this information with the following select in mind. Using a select to show my intention of the JOIN/in-query select or whatever that can do this.
SELECT * FROM invBlueprintTypesPrices
WHERE blueprintTypeID = blueprintType.typeID
ORDER BY timestamp DESC LIMIT 1
And I need the main row from table invBlueprintTypes to still show even if there is no result from the invBlueprintTypesPrices. The LIMIT 1 is because I want the newest row possible, but deleting the older data is not a option since history is needed.
If I've understood correctly I think I need a subquery select, but how to do that? I've tired adding the exact query that is above with a AS blueprintPrices after the query's closing ), but did not work with a error with the
WHERE blueprintTypeID = blueprintType.typeID
part being the focus of the error. I have no idea why. Anyone who can solve this?
You'll need to use a LEFT JOIN to check for NULL values in invBlueprintTypesPrices. To mimic the LIMIT 1 per TypeId, you can use the MAX() or to truly make sure you only return a single record, use a row number -- this depends on whether you can have multiple max time stamps for each type id. Assuming not, then this should be close:
Select
...
From
invBlueprintTypes As blueprints
Inner Join invTypes As blueprintType On blueprints.blueprintTypeID = blueprintType.typeID
Inner Join invTypes As productType On blueprints.productTypeID = productType.typeID
Inner Join invGroups As productGroup On productType.groupID = productGroup.groupID
Inner Join invCategories As productCategory On productGroup.categoryID = productCategory.categoryID
Left Join (
SELECT MAX(TimeStamp) MaxTime, TypeId
FROM invBlueprintTypesPrices
GROUP BY TypeId
) blueprintTypePrice On blueprints.blueprintTypeID = blueprintTypePrice.typeID
Left Join invBlueprintTypesPrices blueprintTypePrices On
blueprintTypePrice.TypeId = blueprintTypePrices.TypeId AND
blueprintTypePrice.MaxTime = blueprintTypePrices.TimeStamp
Where
blueprints.techLevel = 1 And
blueprintType.published = 1 And
productType.marketGroupID Is Not Null And
blueprintType.basePrice > 0
Order By
blueprintTypePrices.profitHour
Assuming you might have the same max time stamp with 2 different records, replace the 2 left joins above with something similar to this getting the row number:
Left Join (
SELECT #rn:=IF(#prevTypeId=TypeId,#rn+1,1) rn,
TimeStamp,
TypeId,
profitHour,
#prevTypeId:=TypeId
FROM (SELECT *
FROM invBlueprintTypesPrices
ORDER BY TypeId, TimeStamp DESC) t
JOIN (SELECT #rn:=0) t2
) blueprintTypePrices On blueprints.blueprintTypeID = blueprintTypePrices.typeID AND blueprintTypePrices.rn=1
You don't say where you are putting the subquery. If in the select clause, then you have a problem because you are returning more than one value.
You can't put this into the from clause directly, because you have a correlated subquery (not allowed).
Instead, you can put it in like this:
from . . .
(select *
from invBLueprintTypesPrices ibptp
where ibtp.timestamp = (select ibptp2.timestamp
from invBLueprintTypesPrices ibptp2
where ibptp.blueprintTypeId = ibptp2.blueprintTypeId
order by timestamp desc
limit 1
)
) ibptp
on ibptp.blueprintTypeId = blueprintType.TypeID
This identifies the most recent records for all the blueprintTypeids in the subquery. It then joins in the one that matches.
I have the following SQL statement
SELECT be.*, it.order_number
FROM songs AS be
INNER JOIN
(
SELECT song_id, order_number
FROM items
WHERE order_status = 1
) it
ON be.id = it.song_id
INNER JOIN orders AS or
ON it.order_number = or.order_number
WHERE be.active = 0
I can't seem to understand why this statement does not produce any results. When I remove the following line;
INNER JOIN orders AS or
ON it.order_number = or.order_number
It seems to produce results, and I know that the order_number does exist in the orders table - so it's clearly incorrect syntax but i'm not sure where to go from here? Appreciate the help.
The problem in this particular instance is that the or in the query is a reserved word. You can use that if you wish, but you'll have to quote it, like so
SELECT be.*, it.order_number
FROM songs AS be
INNER JOIN
(
SELECT song_id, order_number
FROM items
WHERE order_status = 1
) it
ON be.id = it.song_id
INNER JOIN orders AS "or"
ON it.order_number = "or".order_number
WHERE be.active = 0
Generally though, for readability, I'd avoid such names. If you have to quote it or escape it, it's probably a bad name.
I have this query in MySQL:
SELECT pr.*, pr7.value AS `room_price_high`
FROM `jos_hp_properties` pr
LEFT OUTER JOIN `jos_hp_properties2` pr7 ON pr7.property=pr.id
WHERE pr7.field=23
The jos_hp_properties table has 27 rows but the query only returns one. Based on this question I think it may be because of the WHERE clause. The jos_hp_properties2 table has fields id, property, field, value, where field is a foreign key to a third table (which I don't need to get data from).
Is there a way to select all the rows from the first table, including the value from table #2 where the field is 23 (or NULL if there is no field 23)?
Sure. Move the WHERE condition to the JOIN:
SELECT pr.*, pr7.value AS `room_price_high`
FROM `jos_hp_properties` pr
LEFT JOIN `jos_hp_properties2` pr7
ON pr7.property=pr.id
AND
pr7.field=23
You must place the pr7 criteria in the join, not in the where clause. The where clause works on the entire result set AFTER the join has been performed.
SELECT pr.*, pr7.value AS `room_price_high`
FROM `jos_hp_properties` pr
LEFT OUTER JOIN `jos_hp_properties2` pr7 ON pr7.property=pr.id and pr7.field=23
Try this:
SELECT pr.*, pr7.value AS `room_price_high`
FROM `jos_hp_properties` pr
LEFT OUTER JOIN `jos_hp_properties2` pr7 ON pr7.property=pr.id
WHERE (pr7.field=23 OR pr7.field is null)
You can also use a CTE (Common Table Expression) to do the select, then use the CTE to do the left join..
wrc (parentid, childid) as (
select parentid, childid
from placechild
where relationshipid in (select id from placerelationship where relationship = 'Winter Region Capital')
),
stw (cnid, coid, capid, st_or_te, sid, scid,wcid) as (
select s.cnid, s.coid, s.capid, s.st_or_te, s.sid, s.scid, w.childid
from stcap s
left join wrc w
on s.sid = w.parentid
)
select * from stw