I want to update multiple rows based on a SELECT sql query.
I want to do it ALL IN AN SQL SHELL!
Here is my select:
SELECT #myid := id, #mytitle := title
FROM event
WHERE pid>0 GROUP BY title
ORDER BY start;
Then, I want to do an update with this pseudocode:
foreach($mytitle as $t)
BEGIN
UPDATE event
SET pid=$myid
WHERE title=$t;
END
But I don't know how to ake a loop in SQL.
Maybe there's a way to make it in a single sql query?
I DON'T WANT ANY PHP!!! ONLY SQL SHELL CODE!!!
I want to update every rows with a pid with the id of the first occurence of an event. Start is a timestamp
I think this should do what you want, but if it doesn't (I'm not sure about joining a subquery in an UPDATE query) then you can use a temporary table instead.
UPDATE
event
JOIN (
SELECT
MIN(pid) AS minPID,
title
FROM
event
WHERE
pid > 0
GROUP BY
title
) AS findPIDsQuery ON event.title = findPIDsQuery.title
SET
event.pid = findPIDsQuery.minPID
Pure SQL doesn't really have "loops", per se: it's a set-based descriptive language. I believe the following update will do what you want (though your problem statements leaves much to be desired—we know nothing about the underlying schema).
update event t
set pid = ( select min(id)
from event x
where x.title = t.title
and x.pid > 0
group by x.title
having count(*) > 1
)
Cheers!
Related
Is it possible to create a trigger that conditionally updates a column with a random value from another tables column.
Previously I received help to create a trigger that updates a column with a random value from another tables column: MySQL: Trigger Update with random value from another tables column. I’m trying now to make it conditionally based on another columns value.
If the users.selection column = ‘fruits’ then random select from fruits.
If the users.selection column = ‘animals’ then random from animals.
If neither ‘fruits’ nor ‘animals’ don’t update.
Here is a db-fiddle: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=6bc76ed2c104dad0e27dd35b1da112a7
Major thanks to #Akina for getting me this far! Lots to learn.
Update (May 29th):
I still can’t figure it out. I thought maybe I would need a SELECT with IF statement first to return the selection column value but that didn’t seem to work. Basically I have tried a lot of different combinations using these examples below as templates. None of them seem to bring my closer.
Anyone have any ideas?
Examples:
SELECT T1.ID, IFNULL(T1.name, T2.name) AS name
FROM firsttable T1
LEFT JOIN secondtable T2
ON T1.T2_id = T2.id
SET final_price= CASE
WHEN currency=1 THEN 0.81*final_price
ELSE final_price
END
SET col = (
SELECT other_col
FROM other_table
WHERE other_table.table_id = table.id
);
SELECT book_name,isbn_no,
IF((SELECT COUNT(*) FROM book_mast WHERE pub_lang='English')>
(SELECT COUNT(*) FROM book_mast WHERE pub_lang<>'English'),
(CONCAT("Pages: ",no_page)),(CONCAT("Price: ",book_price)))
AS "Page / Price"
FROM book_mast;
I think you need to conditionally define what does what, if selection is fruit, then do something. else if selection is animals, then do another thing.
e.g:
CREATE TRIGGER trigger_test
BEFORE UPDATE
ON users
FOR EACH ROW
BEGIN
IF (NEW.selection = 'fruits') THEN
SET NEW.random = ( SELECT fruits
FROM list
ORDER BY RAND() LIMIT 1 );
ELSEIF (NEW.selection = 'animals') THEN
SET NEW.random = ( SELECT animals
FROM list
ORDER BY RAND() LIMIT 1 );
END IF;
END;
My problem is the following, I want set a list of ID in a variable, then use this variable in a subquery. The problem is that WorkBench (my GUI) return the following error : "subquery returning multiple rows". It seems to me that's what I want.
Please explain me where I am wrong.
This is my query :
set #listID := (select ID_VOIE as ID from voies
where ORIGINE = 'XXX'
group by CODE_INSEE, CODE_VOIE
having count(*) > 1);
select substring(v.CODE_INSEE,1,2), count(*) from voies v
where v.ID_VOIE in (#listID)
group by substring(vs.CODE_INSEE,1,2);
The thing is I'm blocked with the "group by", I want do a groupd by after a first group by, that's why I can't (or at least i didn't find a way) write the request with a single WHERE clause.
The thing is I know that I can put the whole request directly in my subquery instead of using variable but :
It can let me use this trick in another requests that needed this behaviour (DRY concept !)
I'm not sure but the subquery will be executed in each turn of my loop, and that will be very inefficient
So I seek 2 possible ways : a way that let me use a list in a variable in a subquery OR a way that let me use "group by" twice in a single query.
Thanks you in advance for your answers (oh and sorry for my english, this is not my maternal language).
Unless you need that variable for something else, you should be able to skip it entirely as follows:
SELECT
SUBSTRING(v.CODE_INSEE,1,2),
COUNT(*)
FROM
voies v
WHERE
v.ID_VOIE in
(SELECT
ID_VOIE as ID
FROM
voies
WHERE
ORIGINE = 'XXX'
GROUP BY
CODE_INSEE,
CODE_VOIE
HAVING COUNT(*) > 1)
GROUP BY
SUBSTRING(vs.CODE_INSEE,1,2);
As you say, the subquery will be executed for all rows. To avoid that, a variable would be best, but MySQL doesn't support table variables. Instead, you can use a temporary table:
IF EXISTS DROP TABLE myTempTable;
CREATE TEMPORARY TABLE myTempTable (ID_VOIE int); -- I don't know the datatype
INSERT INTO myTempTable (ID_VOIE)
SELECT DISTINCT -- using distinct so I can join instead of use IN.
ID_VOIE as ID from voies
WHERE
ORIGINE = 'XXX'
GROUP BY
CODE_INSEE, CODE_VOIE
HAVING COUNT(*) > 1
And now you can do this:
SELECT
SUBSTRING(v.CODE_INSEE,1,2), COUNT(*)
FROM
voies v
JOIN myTempTable tt ON
v.ID_VOIE = tt.ID_VOIE
GROUP BY SUBSTRING(vs.CODE_INSEE,1,2);
I'm using MySQL 5.6 and I have this issue.
I'm trying to improve my bulk update strategy for this case.
I have a table, called reserved_ids, provided by an external company, to assign unique IDs to its invoices. There is no other way to make this; I can't use auto_increment fields or simulated sequences.
I have this PL pseudocode to make this assignment:
START TRANSACTION;
OPEN invoice_cursor;
read_loop: LOOP
FETCH invoice_cursor INTO internalID;
IF done THEN
LEAVE read_loop;
END IF;
SELECT MIN(SECUENCIAL)
INTO v_secuencial
FROM RESERVED_IDS
WHERE COUNTRY_CODE = p_country_id AND INVOICE_TYPE = p_invoice_type;
DELETE FROM RESERVED_IDS WHERE SECUENCIAL = v_secuencial;
UPDATE MY_INVOICE SET RESERVED_ID = v_secuencial WHERE INVOICE_ID = internalID;
END LOOP read_loop;
CLOSE invoice_cursor;
COMMIT;
So, it's take one - remove - assign, then take next - remove - assign... and so on.
This works, but it's very very slow.
I don't know if there is any approach to make this assignment in a faster way.
I'm looking for something like INSERT INTO SELECT..., but with UPDATE statement, to assign 1000 or 2000 IDs directly, and no one by one.
Please, any suggestion is very helpful for me.
Thanks a lot.
EDIT 1: I have added WHERE clause details, because it was requested by user #vmachan . In the UPDATE...INVOICE clause, I don't filter by other criteria, because I have the direct and indexed invoice ID, which I want to update. Thanks
Finally, I have this solution. It's much faster than my initial approach.
The UPDATE query is
set #a=0;
set #b=0;
UPDATE MY_INVOICE
INNER JOIN
(
select
F.invoice_id,
I.secuencial as RESERVED_ID,
CONCAT_WS(/* format your final invoice ID */) AS FINAL_MY_INVOICE_NUMBER
FROM
(
select if(#a, #a:=#a+1, #a:=1) as current_row, internal_id
from MY_INVOICE
where reserved_id is null
order by internal_id asc
limit 2000
) F
INNER JOIN
(
SELECT if(#b, #b:=#b+1, #b:=1) as current_row, secuencial
from reserved_ids
order by secuencial asc
limit 2000
) I USING (CURRENT_ROW)
) TEMP MY_INVOICE.internal_id=TEMP.INTERNAL_ID
SET MY_INVOICE.RESERVED_ID = TEMP.RESERVED_ID, MY_INVOICE.FINAL_MY_INVOICE_NUMBER=TEMP.FINAL_MY_INVOICE_NUMBER
So, with autogenerated and correlated secuencial numbers #a and #b, we can join two different and no related tables like MY_INVOICE and RESERVED_IDs.
If you want to check this solution, please execute this tricky update following these steps:
Execute #a and then the first inner select in an isolated way: select if(#a, #a:=#a+1, ...
Execute #b and then the second inner select in an isolated way: select if(#b, #b:=#b+1, ...
Execute #a, #b and the big select that builds the TEMP auxiliar table: select F.invoice_id, ...
Execute the UPDATE
Finally, remove the assigned IDs from RESERVED_ID table.
Assignation time reduced drastically. My initial solution was one by one; with this, you assign 2000 (or more) in one single (ok, and a little tricky) update.
Hope this helps.
I want to loop through some records and update them with an ad hoc query in MySql. I have a name field, so I just want to loop though all of them and append a counter to each name, so it will be name1, name2, name3. Most examples I see use stored procs, but I don't need a stored proc.
As a stepping stone on your way to developing an UPDATE statement, first generate a SELECT statement that generates the new name values to your liking. For example:
SELECT t.id
, t.name
, CONCAT(t.name,s.seq) AS new_name
FROM ( SELECT #i := #i + 1 AS seq
, m.id
FROM mytable m
JOIN (SELECT #i := 0) i
ORDER BY m.id
) s
JOIN mytable t
ON t.id = s.id
ORDER BY t.id
To unpack that a bit... the #i is a MySQL user variable. We use an inline view (aliased as i) to initialize #i to a value of 0. This inline view is joined to the table to be updated, and each row gets assigned an ascending integer value (aliased as seq) 1,2,3...
We also retrieve a primary (or unique) key value, so that we can match each of the rows from the inline view (one-to-one) to the table to be updated.
It's important that you understand how that statement is working, before you attempt writing an UPDATE statement following the same pattern.
We can now use that SELECT statement as an inline view in an UPDATE statement, for example:
UPDATE ( SELECT t.id
, t.name
, CONCAT(t.name,s.seq) AS new_name
FROM ( SELECT #i := #i + 1 AS seq
, m.id
FROM mytable m
JOIN (SELECT #i := 0) i
ORDER BY m.id
) s
JOIN mytable t
ON t.id = s.id
ORDER BY t.id
) r
JOIN mytable u
ON u.id = r.id
SET u.name = r.new_name
SQL Fiddle demonstration here:
http://sqlfiddle.com/#!2/a8796/1
I had to extrapolate, and provide a table name (mytable) and a column name for a primary key column (id).
In the SQL Fiddle, there's a second table, named prodtable which is identical to mytable. SQL Fiddle only allows SELECT in the query pane, so in order to demonstrate BOTH the SELECT and the UPDATE, I needed two identical tables.
CAVEAT: be VERY careful in using MySQL user variables. I typically use them only in SELECT statements, where the behavior is very consistent, with careful coding. With DML statements, it gets more dicey. The behavior may not be as consistent in DML, the "trick" is to use a SELECT statement as an inline view. MySQL (v5.1 and v5.5) will process the query for the inline view and materialize the resultset as a temporary MyISAM table.
I have successfully used this technique to assign values in an UPDATE statement. But (IMPORTANT NOTE) the MySQL documentation does NOT specify that this usage or MySQL user variables is supported, or guaranteed, or that this behavior will not change in a future release.
Have the names stored in a table. Do a join against the names and update in the second table you want to.
Thanks
I have a table like this (MySQL 5.0.x, MyISAM):
response{id, title, status, ...} (status: 1 new, 3 multi)
I would like to update the status from new (status=1) to multi (status=3) of all the responses if at least 20 have the same title.
I have this one, but it does not work :
UPDATE response SET status = 3 WHERE status = 1 AND title IN (
SELECT title FROM (
SELECT DISTINCT(r.title) FROM response r WHERE EXISTS (
SELECT 1 FROM response spam WHERE spam.title = r.title LIMIT 20, 1)
)
as u)
Please note:
I do the nested select to avoid the famous You can't specify target table 'response' for update in FROM clause
I cannot use GROUP BY for performance reasons. The query cost with a solution using LIMIT is way better (but it is less readable).
EDIT:
It is possible to do SELECT FROM an UPDATE target in MySQL. See solution here
The issue is on the data selected which is totaly wrong.
The only solution I found which works is with a GROUP BY:
UPDATE response SET status = 3
WHERE status = 1 AND title IN (SELECT title
FROM (SELECT title
FROM response
GROUP BY title
HAVING COUNT(1) >= 20)
as derived_response)
Thanks for your help! :)
MySQL doesn't like it when you try to UPDATE and SELECT from the same table in one query. It has to do with locking priorities, etc.
Here's how I would solve this problem:
SELECT CONCAT('UPDATE response SET status = 3 ',
'WHERE status = 1 AND title = ', QUOTE(title), ';') AS sql
FROM response
GROUP BY title
HAVING COUNT(*) >= 20;
This query produces a series of UPDATE statements, with the quoted titles that deserve to be updated embedded. Capture the result and run it as an SQL script.
I understand that GROUP BY in MySQL often incurs a temporary table, and this can be costly. But is that a deal-breaker? How frequently do you need to run this query? Besides, any other solutions are likely to require a temporary table too.
I can think of one way to solve this problem without using GROUP BY:
CREATE TEMPORARY TABLE titlecount (c INTEGER, title VARCHAR(100) PRIMARY KEY);
INSERT INTO titlecount (c, title)
SELECT 1, title FROM response
ON DUPLICATE KEY UPDATE c = c+1;
UPDATE response JOIN titlecount USING (title)
SET response.status = 3
WHERE response.status = 1 AND titlecount.c >= 20;
But this also uses a temporary table, which is why you try to avoid using GROUP BY in the first place.
I would write something straightforward like below
UPDATE `response`, (
SELECT title, count(title) as count from `response`
WHERE status = 1
GROUP BY title
) AS tmp
SET response.status = 3
WHERE status = 1 AND response.title = tmp.title AND count >= 20;
Is using GROUP BY really that slow ? The solution you tried to implement looks like requesting again and again on the same table and should be way slower than using GROUP BY if it worked.
This is a funny peculiarity with MySQL - I can't think of a way to do it in a single statement (GROUP BY or no GROUP BY).
You could select the appropriate response rows into a temporary table first then do the update by selecting from that temp table.
you'll have to use a temporary table:
create temporary table r_update (title varchar(10));
insert r_update
select title
from response
group
by title
having count(*) < 20;
update response r
left outer
join r_update ru
on ru.title = r.title
set status = case when ru.title is null then 3 else 1;