I want to update the description in table b. In table a I have the newest data. I want to join on all the numbers that are available in table b and update the description. Only the numbers that are available in table b must be updated!
I have this query:
select * from b
left join a.prod_nr = b.prod_nr
But how can i do an update to the fields? And how is the performance because there are updated 8000 rows.
I have table a
prod_nr description
1 test
2 things
3 pc
table b
prod_nr description
1 nothing
3 monitor
output after query in table b:
prod_nr description
1 test
3 pc
update b
join a on a.prod_nr = b.prod_nr
set b.description = a.description
Related
I have a requirement where If a certain conditions matches then I need to apply JOIN otherwise, I don't need to apply it.
for example
A,B and C are tables
so I need to join B and C if the B.id not in (select entityId from A) otherwise there will be no join.
also here A and C don't have common values.
Table A
id entityId name
1 xyz abc
2 bcd z
3 edc x
Table B
id entityId shopRegID
1 bcd z
Table C
id entityId newEntityID ShopNewname
1 xyz xyze abcd
2 e ee sd
now I have condition like this, where I need to get the data from these table ,based on the entityId provided to me.
I need to eliminate all the shops which are not registered(not in table B) but include the shops which are renamed(in table C but not in B)
suppose If I am given ('xyz','bcd','edc')
the output should contains
bcd (because it's in table B)
xyz (because it's in table C)
and these table have very large amount of data(in 100 thousands )
what is the best and performant way to achive this.
You can use left join and coalesce as follows:
select *
from tableA A
left join tableB B on a.entityid = b.entityid
left join tableB C on a.entityid = c.entityid
WHERE coalesce(b.entityid,c.entityid) is not null
It sounds like you want entities from a that are in either of the tables. This suggests exists logic:
select a.*
from a
where exists (select 1 from b where b.entityId = a.entityId) or
exists (select 1 from c where c.entityId = a.entityId)
I have TableA with 5 rows in column siteID ( so 5 different sites).
I have TableB that stores userIDs and which sites they have access to. I need to take all 5 siteIDs from TableA and check to see if any of the siteIDs are NOT in TableB for a specific user.
I'm trying something similar to this pseudocode but not sure how the syntax should go:
SET #invalidSites = (
SELECT COUNT(*)
FROM userSiteAccess AS usa
RIGHT JOIN customer.sitesVsUsers AS cust
ON usa.listOfSites = cust.siteID
WHERE cust.siteID IS NULL);
EXAMPLE:
TABLE A
listOfSites
1
2
3
TableB
userID siteAccess
50 3
The count should return 2 as the list of sites has 2 additional rows (site 1 and site 2) but the user only has access to site 3.
You need to use LEFT JOIN rather than RIGHT JOIN, and you need to specify the user ID in the ON condition.
SELECT COUNT(*)
FROM userSiteAccess AS usa
LEFT JOIN sitesVsUsers AS cust
ON usa.listOfSites = cust.siteID AND cust.userId = 2
WHERE cust.siteID IS NULL
DEMO
With NOT EXISTS:
select count(*) counter
from tablea a
where not exists (
select 1 from tableb
where userid = 50 and siteaccess = a.listofsites
)
I have two tables: table 1 = university and table 2 = school
I added university_id into the table 2 and I need to connect the two tables.
If university_name from table 1 and name from table 2 are identical, get the id from table 1 and replace it onto table 2 university_id
I am very new to sql so if you could explain that would be great. I have also tried the following with no avail!
select a.id,b.name from university as a
inner join school as b on a.university_name = b.name
UPDATE `school` SET `university_id` = a.id WHERE a.university_name = b.name
Something like
UPDATE school a
JOIN university b ON a.university_name = b.name
SET a.university_id = b.id
should work
I cannot run a test right now... Maybe it does give you a hint.
UPDATE `school` s SET `university_id` = (SELECT u.id FROM `university` u WHERE u.name=s.university_name)
You might need to JOIN the school-table within the SELECT statement.
I need to join table_1 and table_2 in MySQL and compare which user has the most winnings. Then update table_2.winner with the user id which has won..
table 1
city user winnings
1 a 99
1 b 0
1 c 50
1 d 2
table 2
city user_1 user_2 winner
1 a b a
1 c d 50
However I'm struggling to figure out how to join the tables thus far I have
SELECT table_1.winnings AS win_a, table_1.winnings AS win_b
FROM table_1, table_2
WHERE table_2.user_1 = table_1.user
AND table_2.user_2 = table_1.user
http://sqlfiddle.com/#!2/c855b/1
You can join against the table multiple times like this:
SELECT IF(user1.winnings > user2.winnings, "user1", "user2")
FROM table_2 games
JOIN table_1 user1 ON games.user_1 = user1.user
JOIN table_1 user2 ON games.user_2 = user2.user
http://sqlfiddle.com/#!2/c855b/16
I just used #skishore's query, a bit fixed, because it is broken for draws. The one that takes draws under consideration would be
SELECT
case when user1.winnings > user2.winnings then user1.user
when user2.winnings > user1.winnings then user2.user
else null
end
FROM table_2 games
JOIN table_1 user1 ON games.user_1 = user1.user
JOIN table_1 user2 ON games.user_2 = user2.user
But apart from this, I still don't get the purpose. I wrote this in comment to #skishore answer, but paste it here also. Consider the case:
User c won 99 matches played with user b, user d on the other hand won 2 matches played with user c. But who will be the winner between c and d? C
The second question is - why do you need this stored in a separate table? Winnings number will be dynamically changing so you would have to create trigger to keep winner column on table2 up to date. Can't you just get winner using this query?
Using the tables below as an example and the listed query as a base query, I want to add a way to select only rows with a max id! Without having to do a second query!
TABLE VEHICLES
id vehicleName
----- --------
1 cool car
2 cool car
3 cool bus
4 cool bus
5 cool bus
6 car
7 truck
8 motorcycle
9 scooter
10 scooter
11 bus
TABLE VEHICLE NAMES
nameId vehicleName
------ -------
1 cool car
2 cool bus
3 car
4 truck
5 motorcycle
6 scooter
7 bus
TABLE VEHICLE ATTRIBUTES
nameId attribute
------ ---------
1 FAST
1 SMALL
1 SHINY
2 BIG
2 SLOW
3 EXPENSIVE
4 SHINY
5 FAST
5 SMALL
6 SHINY
6 SMALL
7 SMALL
And the base query:
select a.*
from vehicle a
join vehicle_names b using(vehicleName)
join vehicle_attribs c using(nameId)
where c.attribute in('SMALL', 'SHINY')
and a.vehicleName like '%coo%'
group
by a.id
having count(distinct c.attribute) = 2;
So what I want to achieve is to select rows with certain attributes, that match a name but only one entry for each name that matches where the id is the highest!
So a working solution in this example would return the below rows:
id vehicleName
----- --------
2 cool car
10 scooter
if it was using some sort of max on the id
at the moment I get all the entries for cool car and scooter.
My real world database follows a similar structure and has 10's of thousands of entries in it so a query like above could easily return 3000+ results. I limit the results to 100 rows to keep execution time low as the results are used in a search on my site. The reason I have repeats of "vehicles" with the same name but only a different ID is that new models are constantly added but I keep the older one around for those that want to dig them up! But on a search by car name I don't want to return the older cards just the newest one which is the one with the highest ID!
The correct answer would adapt the query I provided above that I'm currently using and have it only return rows where the name matches but has the highest id!
If this isn't possible, suggestions on how I can achieve what I want without massively increasing the execution time of a search would be appreciated!
If you want to keep your logic, here what I would do:
select a.*
from vehicle a
left join vehicle a2 on (a.vehicleName = a2.vehicleName and a.id < a2.id)
join vehicle_names b on (a.vehicleName = b.vehicleName)
join vehicle_attribs c using(nameId)
where c.attribute in('SMALL', 'SHINY')
and a.vehicleName like '%coo%'
and a2.id is null
group by a.id
having count(distinct c.attribute) = 2;
Which yield:
+----+-------------+
| id | vehicleName |
+----+-------------+
| 2 | cool car |
| 10 | scooter |
+----+-------------+
2 rows in set (0.00 sec)
As other said, normalization could be done on few levels:
Keeping your current vehicle_names table as the primary lookup table, I would change:
update vehicle a
inner join vehicle_names b using (vehicleName)
set a.vehicleName = b.nameId;
alter table vehicle change column vehicleName nameId int;
create table attribs (
attribId int auto_increment primary key,
attribute varchar(20),
unique key attribute (attribute)
);
insert into attribs (attribute)
select distinct attribute from vehicle_attribs;
update vehicle_attribs a
inner join attribs b using (attribute)
set a.attribute=b.attribId;
alter table vehicle_attribs change column attribute attribId int;
Which led to the following query:
select a.id, b.vehicleName
from vehicle a
left join vehicle a2 on (a.nameId = a2.nameId and a.id < a2.id)
join vehicle_names b on (a.nameId = b.nameId)
join vehicle_attribs c on (a.nameId=c.nameId)
inner join attribs d using (attribId)
where d.attribute in ('SMALL', 'SHINY')
and b.vehicleName like '%coo%'
and a2.id is null
group by a.id
having count(distinct d.attribute) = 2;
The table does not seems normalized, however this facilitate you to do this :
select max(id), vehicleName
from VEHICLES
group by vehicleName
having count(*)>=2;
I'm not sure I completely understand your model, but the following query satisfies your requirements as they stand. The first sub query finds the latest version of the vehicle. The second query satisfies your "and" condition. Then I just join the queries on vehiclename (which is the key?).
select a.id
,a.vehiclename
from (select a.vehicleName, max(id) as id
from vehicle a
where vehicleName like '%coo%'
group by vehicleName
) as a
join (select b.vehiclename
from vehicle_names b
join vehicle_attribs c using(nameId)
where c.attribute in('SMALL', 'SHINY')
group by b.vehiclename
having count(distinct c.attribute) = 2
) as b on (a.vehicleName = b.vehicleName);
If this "latest vehicle" logic is something you will need to do a lot, a small suggestion would be to create a view (see below) which returns the latest version of each vehicle. Then you could use the view instead of the find-max-query. Note that this is purely for ease-of-use, it offers no performance benefits.
select *
from vehicle a
where id = (select max(b.id)
from vehicle b
where a.vehiclename = b.vehiclename);
Without going into proper redesign of you model you could
1) Add a column IsLatest that your application could manage.
This is not perfect but will satisfy you question (until next problem, see not at the end)
All you need is when you add a new entry to issue queries such as
UPDATE a
SET IsLatest = 0
WHERE IsLatest = 1
INSERT new a
UPDATE a
SET IsLatest = 1
WHERE nameId = #last_inserted_id
in a transaction or a trigger
2) Alternatively you can find out the max_id before you issue your query
SELECT MAX(nameId)
FROM a
WHERE vehicleName = #name
3) You can do it in single SQL, and providing indexes on (vehicleName, nameId) it should actually have decent speed with
select a.*
from vehicle a
join vehicle_names b ON a.vehicleName = b.vehicleName
join vehicle_attribs c ON b.nameId = c.nameId AND c.attribute = 'SMALL'
join vehicle_attribs d ON b.nameId = c.nameId AND d.attribute = 'SHINY'
join vehicle notmax ON a.vehicleName = b.vehicleName AND a.nameid < notmax.nameid
where a.vehicleName like '%coo%'
AND notmax.id IS NULL
I have removed your GROUP BY and HAVING and replaced it with another join (assuming that only single attribute per nameId is possible).
I have also used one of the ways to find max per group and that is to join a table on itself and filter out a row for which there are no records that have a bigger id for a same name.
There are other ways, search so for 'max per group sql'. Also see here, though not complete.