I am having a wee problem, and I am sure there is a more convenient/simpler way to achieve the solution, but all searches are throw in up a blanks at the moment !
I have a mysql db that is regularly updated by php page [ via a cron job ] this adds or deletes entries as appropriate.
My issue is that I also need to check if any details [ie the phone number or similar] for the entry have changed, but doing this at every call is not possible [ not only does is seem to me to be overkill, but I am restricted by a 3rd party api call limit] Plus this is not critical info.
So I was thinking it might be best to just check one entry per page call, and iterate through the rows/entires with each successive page call.
What would be the best way of doing this, ie keeping track of which entry/row in the table that the should be checked next?
I have 2 ideas of how to implement this:
1 ) The id of current row could be save to a file on the server [ surely not the best way]
2) an extra boolean field [check] is add to the table, set to True on the first entry and false to all other.
Then on each page call it;
finds 'where check = TRUE'
runs the update check on this row,
'set check = FALSE'
'set [the next row] check = TRUE'
Si this the best way to do this, or does anyone have any better sugestion ?
thanks in advance !
.k
PS sorry about the title
Not sure if this is a good solution, but if I have to make nightly massive updates, I'll write the updates to a new blank table, then do a SQL select to join the tables and tell me where they are different, then do another SQL UPDATE like
UPDATE table, temptable
SET table.col1=temptable.col1, table.col2=temptable.col2 ......
WHERE table.id = temptable.id;
You can store the timestamp that a row is updated implicitly using ON UPDATE CURRENT_TIMESTAMP [http://dev.mysql.com/doc/refman/5.0/en/timestamp.html] or explicitly in your update SQL. Then all you need to do is select the row(s) with the lowest timestamp (using ORDER BY and LIMIT) and you have the next row to process. So long as you ensure that the timestamp is updated each time.
e.g. Say you used the field last_polled_on TIMESTAMP to store the time you polled a row.
Your insert looks like:
INSERT INTO table (..., last_polled_on) VALUES (..., NOW());
Your update looks like:
UPDATE table SET ..., last_polled_on = NOW() WHERE ...;
And your select for the next row to poll looks like:
SELECT ... FROM table ORDER BY last_polled_on LIMIT 1;
Related
We use (INSERT INTO) to insert a record in the table which creates more than one record when used again. Is there any way to add a record and alternately replacing the prevoius one without adding any new record.
I know this would work:
UPDATE Customers
SET ContactName='Alfred Schmidt', City='Hamburg'
WHERE CustomerName='Alfreds Futterkiste';
But what if there is no condition ie. we don't know the record, we only know the column name. Is there any way to fill only one record and alternately replace the previous record without creating 2nd record?
OK... updating if a record exists or creating a record if there are zero records is a pretty simple matter and you have a solution for it. That having been said, I would do something different and keep track of my message of the day by date:
-- This is REALLY BASIC, but, just to give you the idea...
CREATE TABLE [dbo].[MessageOfTheDay](
[MessageDate] [date] not null,
[MessageContents] [nvarchar](500) not null,
UNIQUE (MessageDate)
)
declare #MessageContents nvarchar(500), #MessageDate date
set #MessageContents = 'This is the new MOTD!!!'
set #MessageDate = GETDATE()
-- Every day, create a new record and you can keep track of previous MOTD entries...
insert into MessageOfTheDay(MessageDate, MessageContents)
values (#MessageDate, #MessageContents)
-- Get the message for today
select MessageContents from MessageOfTheDay where MessageDate = #MessageDate
-- If you want, you can now create messages for FUTURE days as well:
set #MessageContents = 'This is tomorrow''s MOTD!!!';
set #MessageDate = dateadd(D, 1,GETDATE())
insert into MessageOfTheDay(MessageDate, MessageContents)
values (#MessageDate, #MessageContents)
-- Get tomorrow's message
select MessageContents from MessageOfTheDay where MessageDate = #MessageDate
-- If you aren't necessarily going to have one per day and want to always just show the most recent entry
select MessageContents from MessageOfTheDay order by MessageDate desc limit 1
Anyway, that's just my $.02. At some point I bet you will want to look over the history of your MOTD and when you do, you will be happy that you have that history. Plus, this more accurately models the data you are trying to represent.
I got my answer and It's working now!
I used:
INSERT INTO data (a, b, c)
VALUES
('1','2','3')
ON DUPLICATE KEY UPDATE c=VALUES(a)+VALUES(b)
I am looking for a way to check if there are certain number of records within mysql table. For example: After POST request been before putting data to dabase, it checks first how many records there are. If lets say there are 24 records, then it will delete record with latest date based on timestamp and then inster new value from POST request. Has anyone got idea on how to do it? Looking forward fpr your answers. Below I attached simple code i wrote to insert data from post request into table.
<?php
include("connect.php");
$link=Connection();
$temp1=$_POST["temp1"];
$hum1=$_POST["hum1"];
$query = "INSERT INTO `tempLog` (`temperature`, `humidity`)
VALUES ('".$temp1."','".$hum1."')";
mysql_query($query,$link);
mysql_close($link);
header("Location: index.php");
?>
When you say delete with the latest date I have to assume you mean the oldest record? Your description doesnt tell me the name of you date field so Lets assume its onDate. You also didnt mention what your primary key is so lets assume that is just id. if you run the below query before inserting it will purge all the oldest records leaving only the newest 23 in the database.
delete from templog where id in (
select id from (
select #rownum:=#rownum+1 'rowid', t.id from templog t, (select #rownum:=0)r order by t.onDate
)v where v.rowid > 23
);
Of course you should test on data you don't mind losing.
It is best to do a cleanup purge each time instead of removing a single row before adding a new one because in the event of exceptions it will never clean itself down to the 24 rows you wish to truly have.
I also want to note that you may want to reconsider this method all together. Instead leave the data there, and only query the most recent 24 when displaying the log. Since you are going through the trouble of collecting the data you might as well keep it for future reporting. Then later down the road if your table gets to large run a simple daily purge query to delete anything older than a certain threshold.
Hope this helps.
I wrote a small script which uses the concept of long polling.
It works as follows:
jQuery sends the request with some parameters (say lastId) to php
PHP gets the latest id from database and compares with the lastId.
If the lastId is smaller than the newly fetched Id, then it kills the
script and echoes the new records.
From jQuery, i display this output.
I have taken care of all security checks. The problem is when a record is deleted or updated, there is no way to know this.
The nearest solution i can get is to count the number of rows and match it with some saved row count variable. But then, if i have 1000 records, i have to echo out all the 1000 records which can be a big performance issue.
The CRUD functionality of this application is completely separated and runs in a different server. So i dont get to know which record was deleted.
I don't need any help coding wise, but i am looking for some suggestion to make this work while updating and deleting.
Please note, websockets(my fav) and node.js is not an option for me.
Instead of using a certain ID from your table, you could also check when the table itself was modified the last time.
SQL:
SELECT UPDATE_TIME
FROM information_schema.tables
WHERE TABLE_SCHEMA = 'yourdb'
AND TABLE_NAME = 'yourtable';
If successful, the statement should return something like
UPDATE_TIME
2014-04-02 11:12:15
Then use the resulting timestamp instead of the lastid. I am using a very similar technique to display and auto-refresh logs, works like a charm.
You have to adjust the statement to your needs, and replace yourdb and yourtable with the values needed for your application. It also requires you to have access to information_schema.tables, so check if this is available, too.
Two alternative solutions:
If the solution described above is too imprecise for your purpose (it might lead to issues when the table is changed multiple times per second), you might combine that timestamp with your current mechanism with lastid to cover new inserts.
Another way would be to implement a table, in which the current state is logged. This is where your ajax requests check the current state. Then generade triggers in your data tables, which update this table.
You can get the highest ID by
SELECT id FROM table ORDER BY id DESC LIMIT 1
but this is not reliable in my opinion, because you can have ID's of 1, 2, 3, 7 and you insert a new row having the ID 5.
Keep in mind: the highest ID, is not necessarily the most recent row.
The current auto increment value can be obtained by
SELECT AUTO_INCREMENT FROM information_schema.tables
WHERE TABLE_SCHEMA = 'yourdb'
AND TABLE_NAME = 'yourtable';
Maybe a timestamp + microtime is an option for you?
I want to get the last affected table name (after insert).
I tried with mysql_insert_id() but i got only id.
I want table name also.
Can anyone give me the idea for my problem
It's a strech... But if :
you are running mysql 5.6.3 +
you still have access to the insert query (let's say it's $query)
you are sure it's an insert query (because, hey, you know you want last_insert_*, don't you?)
You can try:
$row = mysql_fetch_assoc(mysql_query("explain $query"));
$table = $row['table'];
From mysql 5.6.3+ you can combine explain with a insert into query.
This should return only 1 row, I think.
I dont have mysql 5.6.3+ myself to test it.
You can override mysql_query function as defined in this post, save you last call table name in global var or session and pray for last called insert finish last.
// THIS JUST SAMPLE... use code from link below ^
function custom_mysql_query($query){
if(strstr('INSERT',$query)){
/*GET YOUR TABLE NAME WITH REGEX*/
}
basic_mysql_query($query);
}
This is very very very bad solution for me. But in theory will work.
You mention in your comment that you're using a common function to apply the changes in, preventing you from 'knowing' what the last table is you inserted in.
If that's the case: your logic is flawed.
MySQL is not gonna tell you what the last table is it did an INSERT in. You will have to write a hook in your function where you last know what table you're gonna update. No matter what function you use, you must specifiy a table name at some point, before executing the insert. You store the table name at that point.
You can do that in many ways, depending on your needs:
store it in a mysql table (last_updated_table with only 1 column,
for example)
store it in a variable (if you only need it in the
same request)
store it in a session (I wouldn't opt for this)
You can use the information_schema database if you have one :
SELECT TABLE_SCHEMA, TABLE_NAME, UPDATE_TIME
FROM TABLES
ORDER BY UPDATE_TIME DESC
LIMIT 0,1
Use this after your query, and you'll get the affected table.
I have a table which contains a list of cruises, and I want one to be 'Cruise of the Week'
So when the user makes a cruise 'Cruise of the Week' the previous 'Cruise of the Week' is automatically deselected.
Am I on the right lines of running a query to load the existing 'Cruise of the Week' and updating that one at the same time as the new one ? Not sure where to start....
thanks
Rich :)
Mutually exclusive checkbox is called radiobutton
UPDATE cruises SET active=0
UPDATE cruises SET active=1 WHERE id=123
You could add a unique index to active to make sure there is only one active at all time.
This might already do the trick. However, when doing it right this could create a concurrency issue. It is not likely to happen and doesn't create very big issues I think so it is doable without getting into transactions and other things to prevent the concurrency.
It could be done in one query also but don't really like that although it is doable in MySQL, pseudo code:
UPDATE cruises SET active = (CASE WHEN id=123 THEN 1 ELSE 0 END)
You gotta like it. The good thing about one query is that updates concurrency is handles by MySQL but I suspect it to be slower and it is not as clear as 2 queries.
Yep, you're on the right track. Load the existing data and update the record when the user submits the form.
UPDATE cruises
SET active = ( CASE WHEN id = #OldCruiseId THEN 0
WHEN id = #NewCruiseId THEN 1
END
)
WHERE cruise_id IN (#OldCruiseId, #NewCruisedId)
AND user_id = #UserId