Ok, i'm drawing a blank here and in dire need of your help!
3 tables:
matches (id, goals_slot_1, goals_slot_2, won, draw)
teams (id, name, score_for, score_against, won, lost, draw, points)
team-match (junction table) (team_id, match_id)
So what i want to achieve, is to update the 'draw' column in the teams table SET to the 'sum(draw)' of the matches table of the according teams.
The value of 'draw' in the matches table is '1' when it's a draw, '0' when not.
I just can't figure it out anymore. Stuck on it for days...
Can someone put me on the right track?
You would need to use a correlated sub query to get the values from the other tables. Something like:
UPDATE `teams`
SET `draw`=(SELECT SUM(`draw`)
FROM `matches`
WHERE `id` IN (SELECT `match_id`
FROM `team-match`
WHERE `team_id`=`teams`.`id`))
Or even a single sub query with a join:
UPDATE `teams`
SET `draw`=(SELECT SUM(`draw`)
FROM `matches`
JOIN `team-match`
ON `team-match`.`match_id`=`matches`.`id`
WHERE `team-match`.`team_id`=`teams`.`id`)
Both should do the work. I would assume the first is better for performance, but haven't tested and really they should be within a few milliseconds of each other. Other than this, you would need to use php to query the values and update the individual rows. Really though, the won/lost/draw columns could be calculated on the fly with similar performance and you wouldn't have to update the values every match.
Related
I have this problem that's been killing me for a couple days now.
So we have a table of all processed orders.
We have a table for all orders that come in.
We need to effectively cross-reference the orders in the new table that is continually updating against the orders already completely in the primary table so that we don't complete the same order multiple times.
After we get a batch of new orders, this is the query that I currently run in an attempt to cross reference it with the table of completed orders:
$sql = "DELETE
FROM
`orders_new`
WHERE
`order` IN (
SELECT DISTINCT
`order`
FROM
`orders_all`
)
AND `name` IN (
SELECT DISTINCT
`name`
FROM
`orders_all`
)
AND `jurisdiction` IN (
SELECT DISTINCT
`jurisdiction`
FROM
`orders_all`
)";
As you can probably tell, I want to delete rows from the "orders_new" table where a row with the same order, name, and jurisdiction already exists in the "orders_all" table.
Is this the right way to handle this sort of query?
Well, the right way depends on many things.
But first, I do not like your division into two tables. In that case I would introduce a column identfying state, that woul reference a table with possible states. Those would be "new", "in process", "completed". That way you have one order stored as only one record as it should be.
But your query migt be ok, but you should check the performance.
Take a look at: https://sqlperformance.com/2012/12/t-sql-queries/left-anti-semi-join
Not exactly your case but very similar.
Another thing: Why do you use DISTINCT. That would imply that "order" is not a unique identifier.
Based on your edit you identify the order with composite key "order", "name", "jurisdiction". Is this really the key, the whole key and nothing but the key so help you Codd. If not, you could delete a bunch of records. But even so your query would delete an all orders for which the order, name and jurisdiction can be found in table order IN DIFFERENT RECORDS. So your query is false.
Saying that, a variant of your query might be
DELETE order_new
FROM
order_new
INNER JOIN
order_all ON order_all.order = order_new.order
AND order_all.name = order_new.name
AND order_all.jurisdiction = order_new.jurisdiction
But, the real problem is your ER model.
No, your query will delete any record where there are any records with the same order, name, and jurisdiction, even if those records are different from one another. In other words, a row in orders_new will be deleted if one row in order_all has the same order, a different one has the same name, and a third one has the same jurisdiction. You are very very likely to delete way more than you want to. Instead, this would be more appropriate:
DELETE FROM `orders_new`
WHERE (`order`, `name`, jurisdiction`) IN (
SELECT `order`, `name`, `jurisdiction`
FROM `orders_all`
)
or maybe
DELETE FROM `orders_new`
WHERE EXISTS (
SELECT 1
FROM `orders_all` AS oa
WHERE oa.`order` = `orders_new`.`order`
AND oa.`name` = `orders_new`.`name`
AND oa.`jurisdiction` = `orders_new`.`jurisdiction`
)
You should convert that to a DELETE - JOIN construct like
DELETE `orders_new`
FROM `orders_new`
INNER JOIN `orders_all` ON `orders_new`.`order` = `orders_all`.`order`
AND `orders_new`.`name` = `orders_all`.`name`
AND `orders_new`.`jurisdiction` = `orders_all`.`jurisdiction`;
I'm in need about a MySQL query which happens to be far more complicated than any other I have ever made (I can barely use the simpliest queries really).
So, I have 2 tables. One has the columns (user, rank), the other has (user, vote).
In a PHP environment, I need to update the rank of a user in table1 based on the vote contained in table2. Something along the lines of "If user voted 1, add +50 to his rank. If user voted -1, add -50 to his rank. If user voted 2 add +200 to his rank."
I can do all the "if" work in PHP but would really need to have an efficient SQL query to get the data and manipulate the rank, because I'm already full of poorly optimized interrogations in my project.
Thank you so much in advance!
Using an insert...select statements combined with an ON DUPLICATE KEY UPDATE clause, you should be able to do it in one go:
INSERT INTO userrank(user, rank)
SELECT v.user, sum(v.vote) * 50 as rank
FROM uservote v
ON DUPLICATE KEY UPDATE rank = v.rank
You could add a second statement, in case you want to remove a user's rank when all his votes are deleted:
DELETE FROM userrank r
WHERE NOT EXISTS (SELECT 'x' FROM uservote v WHERE v.user = r.user)
I have a voting script which pulls out the number of votes per user.
Everything is working, except I need to now display the number of votes per user in order of number of votes. Please see my database structure:
Entries:
UserID, FirstName, LastName, EmailAddress, TelephoneNumber, Image, Status
Voting:
item, vote, nvotes
The item field contains vt_img and then the UserID, so for example: vt_img4 and both vote & nvotes display the number of votes.
Any ideas how I can relate those together and display the users in order of the most voted at the top?
Thanks
You really need to change the structure of the voting table so that you can do a normal join. I would strongly suggest adding either a pure userID column, or at the very least not making it a concat of two other columns. Based on an ID you could then easily do something like this:
select
a.userID,
a.firstName,
b.votes
from
entries a
join voting b
on a.userID=b.userID
order by
b.votes desc
The other option is to consider (if it is a one to one relationship) simply merging the data into one table which would make it even easier again.
At the moment, this really is an XY problem, you are looking for a way to join two tables that aren't meant to be joined. While there are (horrible, ghastly, terrible) ways of doing it, I think the best solution is to do a little extra work and alter your database (we can certainly help with that so you don't lose any data) and then you will be able to both do what you want right now (easily) and all those other things you will want to do in the future (that you don't know about right now) will be oh so much easier.
Edit: It seems like this is a great opportunity to use a Trigger to insert the new row for you. A MySQL trigger is an action that the database will make when a certain predefined action takes place. In this case, you want to insert a new row into a table when you insert a row into your main table. The beauty is that you can use a reference to the data in the original table to do it:
CREATE TRIGGER Entries_Trigger AFTER insert ON Entries
FOR EACH ROW BEGIN
insert into Voting values(new.UserID,0,0);
END;
This will work in the following manner - When a row is inserted into your Entries table, the database will insert the row (creating the auto_increment ID and the like) then instantly call this trigger, which will then use that newly created UserID to insert into the second table (along with some zeroes for votes and nvotes).
Your database is badly designed. It should be:
Voting:
item, user_id, vote, nvotes
Placing the item id and the user id into the same column as a concatenated string with a delimiter is just asking for trouble. This isn't scalable at all. Look up the basics on Normalization.
You could try this:
SELECT *
FROM Entries e
JOIN Voting v ON (CONCAT('vt_img', e.UserID) = v.item)
ORDER BY nvotes DESC
but please notice that this query might be quite slow due to the fact that the join field for Entries table is built at query time.
You should consider changing your database structure so that Voting contains a UserID field in order to do a direct join.
I'm figuring the Entries table is where votes are cast (you're database schema doesn't make much sense to me, seems like you could work it a little better). If the votes are actually on the Votes table and that's connected to a user, then you should have UserID field in that table too. Either way the example will help.
Lets say you add UserID to the Votes table and this is where a user's votes are stored than this would be your query
SELECT Users.id, Votes.*,
SUM(Votes.nvotes) AS user_votes
FROM Users, Votes
WHERE Users.id = Votes.UserID
GROUP BY Votes.UserID
ORDER BY user_votes
USE ORDER BY in your query --
SELECT column_name(s)
FROM table_name
ORDER BY column_name(s) ASC|DESC
I have a table which has several thousand records.
I want to update all the records which have a duplicate firstname
How can I achieve this with a single query?
Sample table structure:
Fname varchar(100)
Lname varchar(100)
Duplicates int
This duplicate column must be updated with the total number of duplicates with a single query.
Is this possible without running in a loop?
update table as t1
inner join (
select
fname,
count(fname) as total
from table
group by fname) as t2
on t1.fname = t2.fname
set t1.duplicates = t2.total
I have a table which has several thousand records. I want to update all the records which have a duplicate firstname How can I achieve this with a single query?
Are you absolutely sure you want to store the number of the so called duplicates? If not, it's a rather simple query:
SELECT fname, COUNT(1) AS number FROM yourtable GROUP BY fname;
I don't see why you would want to store that number though. What if there's another record inserted? What if there are records deleted? The "number of duplicates" will remain the same, and therefore will become incorrect at the first mutation.
Create the column first, then write a query like:
UPDATE table SET table.duplicates = (SELECT COUNT(*) FROM table r GROUP BY Fname/Lname/some_id)
Maybe this other SO will help?
How do I UPDATE from a SELECT in SQL Server?
You might not be able to do this. You can't update the same table that you are selecting from in the same query.
I am writing a converter to transfer data from old systems to new systems. I am using php+mysql.
I have one table that contains millions records with duplicate entries. I want to transfer that data in a new table and remove all entries. I am using following queries and pseudo code to perform this task
select *
from table1
insert into table2
ON DUPLICATE KEY UPDATE customer_information = concat('$firstName',',','$lastName')
It takes ages to process one table :(
I am pondering that is it possible to use group by and get all grouped record automatically?
Other than going through each record and checking duplicate etc.?
For example
select *
from table1
group by firstName, lastName
insert into table 2 only one record and add all users'
first last name into column ALL_NAMES with comma
EDIT
There are different records for each customers with different information. Each row is called duplicated if first and last name of user is same. In new table, we will just add one customer and their bought product in different columns (we have only 4 products).
I don't know what you are trying to do with customer_information, but if you just want to transfer the non-duplicated set of data from one table to another, this will work:
INSERT IGNORE INTO table2(field1, field2, ... fieldx)
SELECT DISTINCT field1, field2, ... fieldx
FROM table1;
DISTINCT will take care of rows that are exact duplicates. But if you have rows that are only partial duplicates (like the same last and first names but a different email) then IGNORE can help. If you put a unique index on table2(lastname,firstname) then IGNORE will make sure that only the first record with lastnameX, firstnameY from table1 is inserted. Of course, you might not like which record of a pair of partial duplicates is chosen.
ETA
Now that you've updated your question, it appears that you want to put the values of multiple rows into one field. This is, generally speaking, a bad idea because when you denormalize your data this way you make it much less accessible. Also, if you are grouping by (lastname, firstname), there will not be names in allnames. Because of this, my example uses allemails instead. In any event, if you really need to do this, here's how:
INSERT INTO table2(lastname, firstname, allemails)
SELECT lastname, firstname, GROUP_CONCAT(email) as allemails
FROM table1
GROUP BY lastname, firstname;
If they are really duplicate rows (every field is the the same) then you can use:
select DISTINCT * from table1
instead of :
select * from table1