I have a check-in / check-out system which writes for every check-in a new row in my table and updates the table when the person checks out (like checkedout = 1)
Now I'm making a new site that always shows the newest checked in person. I do it by polling and storing the highest ID on a variable on that page. In the polling I search for entries > the id i stored. It's working good so far.
But now I want to extend it and show either the latest checked in person OR the latest checked out person. How can I get the last "updated" row in my table?
You can add a column for ex. date_checked of type datetime and update it whenever something happens.
After that just select by that column.
use mysql function called mysqli_insert_id() which will give you last inserted primary key value of the table
try this:
SET #update_id := 0;
UPDATE some_table SET column_name = 'value', id = (SELECT #update_id := id)
WHERE some_other_column = 'blah' LIMIT 1;
SELECT #update_id;
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I have an auto increment column. I want to change value of another column based on this auto increment column value.
another column value ==> (auto increment column value/3) +1
How do I do it via query? Is it possible?
I want to do it for newly creating rows.
Is the new (id/3)+1) value ever going to change?
Judging from the question, the data only exists at the time of the insert. The auto increment column will never change as it has to be a Primary Key, I would only insert on it if you have to join on it or if it is going to change in future. You can get this derived value from a SELECT query after your insert.
SELECT id, ((id/3)+1) as derived value from table;
It is a "derived" value and you should consider not to store this value but calculate it in your PHP code every time you need it. Here is a post where you can find further explanations about when to store derived values: Storing “derived” values vs calculating them on extraction
#Octopi solution could solve your problem.
Try the following:
INSERT INTO your_table (your_column)
SELECT (MAX(auto_increment_column) / 3) + 2 FROM your_table;
EDIT
If you want to calculate the column depending on the number of values use this:
INSERT INTO your_table (your_column)
SELECT (COUNT(*) / 3) + 2 FROM your_table;
EDIT 2
You can accomplish the same using:
INSERT INTO your_table (your_column) VALUES (
(SELECT (MAX(aa.auto_increment_column) / 3) + 2 FROM your_table AS aa)
);
EDIT 3
For more columns you can use something like this:
INSERT INTO your_table (your_column, some_other_column) VALUES (
(SELECT (MAX(aa.auto_increment_column) / 3) + 2 FROM your_table AS aa), some_other_column
);
You can find more info here:
Select from same table as an Insert or Update
In fact you have to add +2 because it's 1 from you rule and +1 to increment the MAX(id).
I'm currently using:
SELECT MAX(id) FROM table
To discover the current id of a certain table, but i heard this can bring bad results. What is the proper way of doing that? Please, notice that i'm not INSERTING or DELETING anything before that query. I just want to know the current ID, without prior INSERT or DELETE.
Perform the following SQL:
SHOW TABLE STATUS LIKE 'TABLENAME'
Then check field AUTO_INCREMENT
You can use the following query:
SELECT id FROM table ORDER BY id DESC LIMIT 1;
Simply put, how can I count how many rows there are before a certain row. I'm using incremental ID's, but rows are deleted a random, so just checking to see what the ID is won't work.
If I have, say, 30 rows, and I've selected one based on a name (or anything really), how many rows are there before that one? It could be 16, 1, 12, or anything.
I'm using MySQL and CodeIgniter.
I assume your primary key column has datatype integer
SELECT COUNT(*) FROM `table`
WHERE id < (SELECT id FROM `table` WHERE `conditions are met for specific row`)
Assuming it's an auto_increment column, deleted rows won't be filled in again so this should do the job.
SELECT COUNT(*) FROM table WHERE id_column < your_selected_row_id;
On your model:
$id = $this->db->get('users')->where("name", "John")->id;
$rows = $this->db->get('users')->where("id < ", $id)->num_rows();
return $rows;
Notice how I'm using "chained methods" and for that you need PHP5 which is the default for CI 2.
You first need to get the ID of the record you need to start counting "backwards" which is the first line, considering a table called users and that the column you are filtering is "name" and the row you want to find has the name value of John.
The second line will give you the number of rows that the query "where id < number" returned where number is the ID you got from the first query. Maybe you can even chain both lines.
How do I get the ID of the last updated row in MySQL using PHP?
I've found an answer to this problem :)
SET #update_id := 0;
UPDATE some_table SET column_name = 'value', id = (SELECT #update_id := id)
WHERE some_other_column = 'blah' LIMIT 1;
SELECT #update_id;
EDIT by aefxx
This technique can be further expanded to retrieve the ID of every row affected by an update statement:
SET #uids := null;
UPDATE footable
SET foo = 'bar'
WHERE fooid > 5
AND ( SELECT #uids := CONCAT_WS(',', fooid, #uids) );
SELECT #uids;
This will return a string with all the IDs concatenated by a comma.
Hm, I am surprised that among the answers I do not see the easiest solution.
Suppose, item_id is an integer identity column in items table and you update rows with the following statement:
UPDATE items
SET qwe = 'qwe'
WHERE asd = 'asd';
Then, to know the latest affected row right after the statement, you should slightly update the statement into the following:
UPDATE items
SET qwe = 'qwe',
item_id=LAST_INSERT_ID(item_id)
WHERE asd = 'asd';
SELECT LAST_INSERT_ID();
If you need to update only really changed row, you would need to add a conditional update of the item_id through the LAST_INSERT_ID checking if the data is going to change in the row.
This is officially simple but remarkably counter-intuitive. If you're doing:
update users set status = 'processing' where status = 'pending'
limit 1
Change it to this:
update users set status = 'processing' where status = 'pending'
and last_insert_id(user_id)
limit 1
The addition of last_insert_id(user_id) in the where clause is telling MySQL to set its internal variable to the ID of the found row. When you pass a value to last_insert_id(expr) like this, it ends up returning that value, which in the case of IDs like here is always a positive integer and therefore always evaluates to true, never interfering with the where clause. This only works if some row was actually found, so remember to check affected rows. You can then get the ID in multiple ways.
MySQL last_insert_id()
You can generate sequences without calling LAST_INSERT_ID(), but the
utility of using the function this way is that the ID value is
maintained in the server as the last automatically generated value. It
is multi-user safe because multiple clients can issue the UPDATE
statement and get their own sequence value with the SELECT statement
(or mysql_insert_id()), without affecting or being affected by other
clients that generate their own sequence values.
MySQL mysql_insert_id()
Returns the value generated for an AUTO_INCREMENT column by the
previous INSERT or UPDATE statement. Use this function after you have
performed an INSERT statement into a table that contains an
AUTO_INCREMENT field, or have used INSERT or UPDATE to set a column
value with LAST_INSERT_ID(expr).
The reason for the differences between LAST_INSERT_ID() and
mysql_insert_id() is that LAST_INSERT_ID() is made easy to use in
scripts while mysql_insert_id() tries to provide more exact
information about what happens to the AUTO_INCREMENT column.
PHP mysqli_insert_id()
Performing an INSERT or UPDATE statement using the LAST_INSERT_ID()
function will also modify the value returned by the mysqli_insert_id()
function.
Putting it all together:
$affected_rows = DB::getAffectedRows("
update users set status = 'processing'
where status = 'pending' and last_insert_id(user_id)
limit 1"
);
if ($affected_rows) {
$user_id = DB::getInsertId();
}
(FYI that DB class is here.)
This is the same method as Salman A's answer, but here's the code you actually need to do it.
First, edit your table so that it will automatically keep track of whenever a row is modified. Remove the last line if you only want to know when a row was initially inserted.
ALTER TABLE mytable
ADD lastmodified TIMESTAMP
DEFAULT CURRENT_TIMESTAMP
ON UPDATE CURRENT_TIMESTAMP;
Then, to find out the last updated row, you can use this code.
SELECT id FROM mytable ORDER BY lastmodified DESC LIMIT 1;
This code is all lifted from MySQL vs PostgreSQL: Adding a 'Last Modified Time' Column to a Table and MySQL Manual: Sorting Rows. I just assembled it.
Query :
$sqlQuery = "UPDATE
update_table
SET
set_name = 'value'
WHERE
where_name = 'name'
LIMIT 1;";
PHP function:
function updateAndGetId($sqlQuery)
{
mysql_query(str_replace("SET", "SET id = LAST_INSERT_ID(id),", $sqlQuery));
return mysql_insert_id();
}
It's work for me ;)
SET #uids := "";
UPDATE myf___ingtable
SET id = id
WHERE id < 5
AND ( SELECT #uids := CONCAT_WS(',', CAST(id AS CHAR CHARACTER SET utf8), #uids) );
SELECT #uids;
I had to CAST the id (dunno why)... or I cannot get the #uids content (it was a blob)
Btw many thanks for Pomyk answer!
Hey, I just needed such a trick - I solved it in a different way, maybe it'll work for you. Note this is not a scalable solution and will be very bad for large data sets.
Split your query into two parts -
first, select the ids of the rows you want to update and store them in a temporary table.
secondly, do the original update with the condition in the update statement changed to where id in temp_table.
And to ensure concurrency, you need to lock the table before this two steps and then release the lock at the end.
Again, this works for me, for a query which ends with limit 1, so I don't even use a temp table, but instead simply a variable to store the result of the first select.
I prefer this method since I know I will always update only one row, and the code is straightforward.
ID of the last updated row is the same ID that you use in the 'updateQuery' to found & update that row. So, just save(call) that ID on anyway you want.
last_insert_id() depends of the AUTO_INCREMENT, but the last updated ID not.
My solution is , first decide the "id" ( #uids ) with select command and after update this id with #uids .
SET #uids := (SELECT id FROM table WHERE some = 0 LIMIT 1);
UPDATE table SET col = 1 WHERE id = #uids;SELECT #uids;
it worked on my project.
Further more to the Above Accepted Answer
For those who were wondering about := & =
Significant difference between := and =, and that is that := works as a variable-assignment operator everywhere, while = only works that way in SET statements, and is a comparison operator everywhere else.
So SELECT #var = 1 + 1; will leave #var unchanged and return a boolean (1 or 0 depending on the current value of #var), while SELECT #var := 1 + 1; will change #var to 2, and return 2.
[Source]
If you are only doing insertions, and want one from the same session, do as per peirix's answer. If you are doing modifications, you will need to modify your database schema to store which entry was most recently updated.
If you want the id from the last modification, which may have been from a different session (i.e. not the one that was just done by the PHP code running at present, but one done in response to a different request), you can add a TIMESTAMP column to your table called last_modified (see http://dev.mysql.com/doc/refman/5.1/en/datetime.html for information), and then when you update, set last_modified=CURRENT_TIME.
Having set this, you can then use a query like:
SELECT id FROM table ORDER BY last_modified DESC LIMIT 1;
to get the most recently modified row.
No need for so long Mysql code. In PHP, query should look something like this:
$updateQuery = mysql_query("UPDATE table_name SET row='value' WHERE id='$id'") or die ('Error');
$lastUpdatedId = mysql_insert_id();