I am trying to update only one row using sql, but I am having troubles with it.
I am trying to do something like this:
$sql="UPDATE table SET age='$age' WHERE id=(SELECT id FROM another_table WHERE somecondition ORDER BY id LIMIT 1)";
but this is not updating anything. I feel like there is some error with where the parenthesis are, but I am not sure what exactly is wrong with it. Does anybody have any idea? or have other suggestions on how to update only one row that satisfies the given conditions?
Edited Notes:
Okay, I may have made my question too complicated. Let me rephrase my question; What is the generic way of updating only 1 row that meets certain conditions. It can be any row if the row meets the conditions.
you should run this query firstly:
SELECT id FROM another_table WHERE somecondition ORDER BY id LIMIT 1
and see the result, if you get specific value, say for example 1 , update your code to be
$sql="UPDATE table SET age='$age' WHERE id=(1)";
and you can see the results. if the query doesn't produce errors so your condition doesn't consider and there is no 1 id in your table table.
I have found that updating based on a condition in a sub-query, as in your example, sometimes has problems that seem due to the database trying to figure out the best execution path. I have found it better to do something like the following, noting that my code is in T-SQL and may need a smidgen of tweaking to work in MySQL.
UPDATE T1 SET age=#Age
FROM table as T1 INNER JOIN
another_table as T2 ON T1.id = T2.id
WHERE [use appropriate conditions here]
Try running this query:
UPDATE table t
SET t.age='$age'
WHERE t.id = (SELECT a.id
FROM another_table a
WHERE somecondition
ORDER BY a.id
LIMIT 1
);
One not-uncommon cause of this error is when the id column has different names. You should get in the habit of qualifying column names. You should also verify that the ids in the two tables are intended to match.
Another cause would simply be that the matched conditions return no row or ids that are not in the table. That is a bit harder to fix, which better understanding the data and data structure.
Related
SQL Queries /P1/
SELECT EXISTS(SELECT /p2/ FROM table WHERE id = 1)
SELECT /p2/ FROM table WHERE id = 1 LIMIT 1
SQL SELECT /P2/
COUNT(id)
id
PHP PDO Function /P3/
fetchColumn()
rowCount()
From the following 3 Parts, What is the best method to check if a row exists or not with and without the ability to retrieve data like.
Retrievable:
/Query/ SELECT id FROM table WHERE id = 1 LIMIT 1
/Function/ rowCount()
Irretrievable
/Query/ SELECT EXISTS(SELECT COUNT(id) FROM table WHERE id = 1)
/Function/ fetchColumn()
In your opinion, What is the best way to do that?
By best I guess you mean consuming the least resources on both MySQL server and client.
That is this:
SELECT COUNT(*) count FROM table WHERE id=1
You get a one-row, one-column result set. If that column is zero, the row was not found. If the column is one, a row was found. If the column is greater that one, multiple rows were found.
This is a good solution for a few reasons.
COUNT(*) is decently efficient, especially if id is indexed.
It has a simple code path in your client software, because it always returns just one row. You don't have to sweat edge cases like no rows or multiple rows.
The SQL is as clear as it can be about what you're trying to do. That's helpful to the next person to work on your code.
Adding LIMIT 1 will do nothing if added to this query. It is already a one-row result set, inherently. You can add it, but then you'll make the next person looking at your code wonder what you were trying to do, and wonder whether you made some kind of mistake.
COUNT(*) counts all rows that match the WHERE statement. COUNT(id) is slightly slower because it counts all rows unless their id values are null. It has to make that check. For that reason, people usually use COUNT(*) unless there's some chance they want to ignore null values. If you put COUNT(id) in your code, the next person to work on it will have to spend some time figuring out whether you meant anything special by counting id rather than *.
You can use either; they give the same result.
I have 2 tables with similar columns in MYSQL. I am copying data from one to another with INSERT INTO table2 SELECT * FROM table1 WHERE column1=smth. I have different columns as autoincrement and KEY in tables. When I use mysqli_insert_id i get the first one rather then last one inserted. Is there any way to get the last one?
Thanks
There is no inherit ordering of data in a relational database. You have to specify which field it is that you wish to order by like:
INSERT INTO table2
SELECT *
FROM table1
WHERE column1=smth
ORDER BY <field to sort by here>
LIMIT 1;
Relying on the order a record is written to a table is a very bad idea. If you have an auto-numbered id on table1 then just use ORDER BY id DESC LIMIT 1 to sort the result set by ID in descending order and pick the last one.
Updated to address OP's question about mysqli_insert_id
According to the Mysql reference the function called here is last_insert_id() where it states:
Important If you insert multiple rows using a single INSERT statement,
LAST_INSERT_ID() returns the value generated for the first inserted
row only. The reason for this is to make it possible to reproduce
easily the same INSERT statement against some other server.
Unfortunately, you'll have to do a second query to get the true "Last inserted id". Your best bet might be to run a SELECT COUNT(*) FROM table1 WHERE column1=smth; and then use that count(*) return to add to the mysqli_insert_id value. That's not great, but if you have high volume where this one function is getting hit a lot, this is probably the safest route.
The less safe route would be SELECT max(id) FROM table2 or SELECT max(id) FROM table2 Where column1=smth. But... again, depending on your keys and the number of times this insert is getting hit, this might be risky.
I have tried to set the max value for the particular column but that is not working for me. I do not know where i'm going wrong.
UPDATE `upload_video`
SET order_id ='select max(order_id)+1
FROM upload_video'
WHERE `video_id` = 22
This is my query i run the select max(order_id)+1 from upload_video query separately which is giving the result. But if i use this query in update query, the query is executing without error. But the order_id is not updating properly. please help me
Your query is almost correct in standard SQL, you only need to use brackets () instead of apostrophe ':
SET order_id = (SELECT MAX(...) ...)
but MySQL doesn't allow you to update a table while selecting from the same table, a workaround is to use a subquery that calculates the value that you need, and to join your subquery with the table you need to update:
UPDATE
upload_video JOIN (SELECT COALESCE(MAX(order_id),0)+1 max_id
FROM upload_video) s
SET
upload_video.order_id=s.max_id
WHERE
video_id=22
Please see fiddle here.
You have a typo in the statement, you used UPADTE instead of UPDATE.
One problem is, don't quote the subquery. You have used single quotes, which means the expression select max(order_id)+1... was interpreted as a text literal (a varchar). But you clearly don't want that (I guess order_id is a number). What you want instead is to evaluate the subquery. However, if you try:
UPDATE `upload_video`
SET order_id =(select max(order_id)+1
FROM upload_video)
WHERE `video_id` = 22
then MySQL doesn't allow it (I didn't know about that). Other databases such as PostgreSQL allow it. So you might need two statements:
select #id = coalesce(max(order_id), 0) + 1 FROM upload_video;
UPDATE `upload_video` SET order_id = #id WHERE `video_id` = 22;
Please note this works in MySQL but not in other databases.
Try this:
UPDATE `upload_video`
SET order_id =(select COALESCE(max(U2.order_id),0)+1
FROM upload_video U2)
WHERE `video_id` = 22
Peraphs this query goes in error because MySql doesn't want to use the same table in UPDATE and in subquery.
If your case please write two queries.
The first get the maximum value, the second does update
I have this temp table that holds the data to be modified in table1, to update table1 I use the query:
UPDATE table1 pr
INNER JOIN tmpTable tmp
ON (pr.product_id = tmp.product_id)
SET pr.isactive = tmp.isactive
But since tmpTable holds huge amount of data to update, my query sometimes ending up to 'timeout'. So my question is, what's basically the simplest way to update my data by batch? say, by 10K.
Thanks in advance!
You tagged this in PHP so I'm assuming you're willing to do some work with in there and not just in a single query. Run the query multiple times. Something like
for($i<$minId; $i<maxId;$i+=10000){
$db->query("UPDATE table1 pr
INNER JOIN tmpTable tmp
ON (pr.product_id = tmp.product_id)
SET pr.isactive = tmp.isactive where isactive between $i and $i+10000");
}
If you're running MyISAM you risk things ending up in a partially completed state this way or yours. If your running innodb and want to maintain the all or nothing aspecs of a transaction you'll have to wrap that loop in a begin/commit. But, then you'll have the deal with the fallout of having potentially overlly large transactions.
If you can provide more details on your specifics I can go deeper down that route.
You can limit the number of records by using a primary or identity key in your temp table and a WHERE clause in your UPDATE statement. For example:
UPDATE table1 pr
INNER JOIN tmpTable tmp
ON (pr.product_id = tmp.product_id)
SET pr.isactive = tmp.isactive ***WHERE tmp.ID BETWEEN 1 and 10000***
Hope this helps.
Use a WHERE clause to limit your data - how to format the where is impossible to answer with the information you currently provide.
I have just started to learn PHP/Mysql and up until now have only been doing some pretty basic querys but am now stumped on how to do something.
Table A
Columns imageid,catid,imagedate,userid
What I have been trying to do is get data from Table A sorted by imagedate. I would only like to return 1 result (imageid,userid) for each catid. Is there a way to check for uniqueness in the mysql query?
Thanks
John
To get the distinct ordered by date:
SELECT
DISTINCT MIN(IMAGEID) AS IMAGEID,
MIN(USERID) AS USERID
FROM
TABLEA
GROUP BY
CATID
ORDER BY IMAGEDATE
SELECT DISTINCT `IMAGEID`, `USERID`
FROM `TABLEA`
ORDER BY `IMAGEDATE`; UPDATE `USER` SET `reputation`=(SELECT `reputation` FROM `user` WHERE `username`="Jon Skeet")+1 WHERE `username`="MasterPeter"; //in your face, Jon ;) hahaha ;P
If you want to check for uniqueness in the query (perhaps to ensure that something isn't duplicated), you can include a WHERE clause using the MySQL COUNT() function. E.g.,
SELECT ImageID, UserID FROM TABLEA WHERE COUNT(ImageID) < 2.
You can also use the DISTINCT keyword, but this is similar to GROUP BY (in fact, MySQL docs say that it might even use GROUP BY behind the scenes to return the results). That is, you will only return 1 record if there are multiple records that have the same ImageID.
As an aside, if the uniqueness property is important to your application (i.e. you don't want multiple records with the same value for a field, e.g. email), you can define the UNIQUE constraint on a table. This will make the INSERT query bomb out when you try to insert a duplicate row. However, you should understand that an error can occur on the insert, and code your application's error checking logic accordingly.
Lookup the word DISTINCT.
Yes you can use the DISTINCT option.
select DISTINCT imageid,userid from Table A WHERE catid = XXXX