I want to update the precalculated order of items in a MySQL table in this way
SET #order_item := 1;
UPDATE item
SET item_order := (#order_item := #order_item + 1)
WHERE
id IN (8,2,1,10);
My expected result is:
id, item_order
8, 1
2, 2
1, 3
10, 4
but as MySQL uses PRIMARY KEY index in id to perform the update, I get:
id, item_order
1, 1
2, 3
8, 3
10, 4
I am wondering if you guys know any workaround to face this problem and keep MySQL using the index in a single update. I happen just do it by performing a lot of UPDATES in a PHP bucle. Ideas?
Thanks!
Try ordering it like this.
SET #order_item := 1;
UPDATE item
SET item_order := (#order_item := #order_item + 1)
WHERE
id IN (8,2,1,10)
order by FIELD(id,8,2,1,10);
You can append an ORDER BY clause to your UPDATE query to tell MySQL the order you want it to process the rows. Of course, you need to be able to SELECT the rows in the desired order using the same ORDER BY clause.
But I guess the order is just what you want to achieve :-(
Related
I need to generate unique "ids", the catch is, it can be only between 1 - 99999.
The "good" thing is, that it has to be unique only in group with another column.
We have groups, each group has its own "group_id" and each group need something like unique('group_id', 'increment_id')
The 99999 records is enough for several years for each group right now, but it is not enough for all groups together, therefore I cant just create table with AUTO_INCREMENT and inserting there records and taking its auto increment.
For example, if I need 5 records for Group one and three records for Group two, I suppose to get something like this:
group_id, increment_id
1, 1,
1, 2,
1, 3,
1, 4,
1, 5,
2, 1
2, 2,
2, 3
Also, the conflict is not an option, therefore using something like "length" can be tricky, if done programatically (there can be i.e. 10 requests at once, each of them first select length for given group_id and then tries to create 10 rows with same increment_id)
However I am thinking - if I set it up as the value of subselect of count, than it will always be "ok"?
You can create a auxiliar table named counters to manage that:
table: counters
columns: group_id, current_counter
OR
Each time you insert a row increment_id = select max(increment_id)+1 from table_xxx where group_id = group_xxxx
You can use user variables to get the incrementing number within each group_id:
select
t.*,
#rn := if(#group_id = group_id,
#rn + 1,
if(#group_id := group_id, 1, 1)
) increment_id
from (
select group_id
from your_table t
/* some where clauses */
order by group_id
) t
cross join (
select #rn := 0,
#group_id := - 1
) t2
I'm coding a movie search engine called Movieovo, I want to select the top 5 rows (movie links) from each group (movie title), but I met a problem in this SQL query:
SELECT link_movie_id, link_id,
#num := if(#link_movie_id = link_movie_id, #num + 1, 1) as row_number,
#link_movie_id := link_movie_id as dummy
FROM link GROUP BY link_movie_id, link_id HAVING row_number <= 5 LIMIT 30
Result: ( Too many characters so I upload as an image )
http://i.imgur.com/phFzUF1.png
You can see "row_number" does not +1 each time
I tried directly in MySQL command line shows me the same results, can anyone help me? I have already wasted 5 hours in this problem..
You are incrementing link_movie_id by 1, but you are grouping by link_movie_id and link_id. With the effect, for some link_movie_id, there are multiple values of link_id in the result. If you are want to get what you are looking for, either group by a single field, or increment it based on a concatenated combination of link_movie_id and link_id.
I'm having a trouble with something that looks like simple thing. I'm trying to find first row that satisfies WHERE part of query and UPDATE it.
UPDATE Donation SET Available=0 WHERE Available != 0 and BloodGroup='" + bloodGroup + "' LIMIT 1"
bloodGroup is variable that gets filled automatically using C# and it keeps string value of selected blood group.
When I try to run this I get incorrect syntax near 'limit'.
What I'm doing wrong? Is it possible using LIMIT like during UPDATE query?
During debugging I got query like this:
UPDATE Donation SET Available=0 WHERE Available != 0 AND BloodGroup='AB-' LIMIT 1
Because C# is often used with SQL Server, perhaps the question is mistagged. The syntax looks fine for MySQL.
In SQL Server, you can do this as:
UPDATE TOP (1) Donation
SET Available = 0
WHERE Available <> 0 AND BloodGroup = 'AB-';
Note that this chooses an arbitrary matching row, as does your original query (there is no order by).
It is not safe to use limit in update queries.
Please refer
http://bugs.mysql.com/bug.php?id=42415
The documentation states that any UPDATE statement with LIMIT clause is considered unsafe since the order of the rows affected is not defined: http://dev.mysql.com/doc/refman/5.1/en/replication-features-limit.html
However, if "ORDER BY PK" is used, the order of rows is defined and such a statement could be logged in statement format without any warning.
You can use like this way limit in Update Queries like these
UPDATE messages SET test_read=1
WHERE id IN (
SELECT id FROM (
SELECT id FROM messages
ORDER BY date_added DESC
LIMIT 5, 5
) tmp
);
Also please
Can you try it? way of getting row_number
UPDATE Donation d1 join (SELECT id,(SELECT #Row:=0) as row,(#Row := #Row + 1) AS row_number FROM Donation where Available <> 0 AND BloodGroup='AB-') d2
ON d1.id=d2.id
SET d1.Available='three'
WHERE d1.Available <> 0 AND d1.BloodGroup='AB-' AND d2.row_number='1'
My Ruby plugin acts_as_list for sorting generates gaps in the position column when I insert Thing 2.0 at position 2 of a list from 1-3 and I want to get this list.
formatted_position;position;name
1;1;Thing 1
2;2;Thing 2.0;
3;4;Thing 2
4;5;Thing 3
So I tried ...
UPDATE user_ranking_items JOIN (SELECT #rownum := 0) r SET formatted_position = #rownum := #rownum + 1 WHERE ranking_id = 1 ORDER BY position ASC
But I got the MySQL exception Incorrect usage of UPDATE and ORDER BY.
How to handle this?
P.S.: Selecting works and returns the list from above ...
SELECT position, #rownum := #rownum + 1 AS formatted_position FROM user_ranking_items JOIN (SELECT #rownum := 0) r WHERE ranking_id = 1 ORDER BY position ASC;
The "trick" is to wrap your query that's working (with the user variable and the order by) as an inline view (MySQL calls it a derived table). Reference that whole view as a row source in the UPDATE statement.
Since you've already got the query that returns the result you want, you just need to have it return a unique id (e.g. the primary key) so you can do the JOIN between the inline view back to the original row in the target of the UPDATE.
Something like this:
UPDATE user_ranking_items t
JOIN (
-- your query here
) s
ON s.id = t.id
SET t.col = s.new_col_val
(This works because MySQL first materializes that inline view, as a temporary MyISAM table, and then the UPDATE references the temporary MyISAM table.)
i have simple query:
SELECT data FROM table WHERE id IN (5, 2, 8, 1, 10)
Question is, how can i select my data and order it like in my IN.
Order must be 5, 2, 8, 1, 10.
Problem is that i have no key for order. IN data is from other query (1), but i need to safe order.
Any solutions?
(1)
SELECT login
FROM posts
LEFT JOIN users ON posts.post_id=users.id
WHERE posts.post_n IN (
2280219,2372244, 2345146, 2374106, 2375952, 2375320, 2371611, 2360673, 2339976, 2331440, 2279494, 2329266, 2271919, 1672114, 2301856
)
Thanx for helping, solutions works but very slow, maybe find something better later, thanx anyway
The only way I can think to order by an arbitrary list would be to ORDER BY comparisons to each item in that list. It's ugly, but it will work. You may be better off sorting in whatever code you are doing the selection.
SELECT data FROM t1 WHERE id IN (5, 2, 8, 1, 10)
ORDER BY id = 10, id = 1, id = 8, id = 2, id = 5
The order is reversed because otherwise you would have to add DESC to each condition.
You can use a CASE statement
SELECT data
FROM table WHERE id IN (5, 2, 8, 1, 10)
ORDER BY CASE WHEN id = 5 THEN 1 WHEN id = 2 THEN 2 WHEN id = 8 THEN 3 WHEN id = 1 THEN 4 WHEN id = 10 THEN 5 END
SELECT data FROM table
WHERE id IN (5, 2, 8, 1, 10)
ORDER BY FIELD (id, 5, 2, 8, 1, 10)
http://dev.mysql.com/doc/refman/5.5/en/string-functions.html#function_field
Might be easier to auto-generate (because it basically just needs inserting the wanted IDs comma-separated in the same order a second time) than the other solutions suggested using CASE or a number of ID=x, ID=y ...
http://sqlfiddle.com/#!2/40b299/6
I think that's what you're looking for :D Adapt it to your own situation.
To do this dynamically, and within MySql, I would suggest to do the following:
Create a temp table or table variable (not sure if MySql has these), with two columns:
OrderID mediumint not null auto_increment
InValue mediumint -(or whatever type it is)
Insert the values of the IN clause in order, which will generate ID's in order of insertion
Add a JOIN to your query on this temp table
Change your Order By to be
order by TempTable.OrderID
Drop temp table (again, in SQL inside a stored proc, this is automatic, not sure about MySql so mentioning here for full disclosure)
This effectively circumvents the issue of you not having a key to order by in your table ... you create one. Should work.