Is it possible to retrieve the entries from a Partition when the Partition-id is given?
For example : If I enter the Partition-id as 3 , Can I get the entries in that particular partition only?
Please Help.!
No, current API does not support this.
Related
Trying to create a table which stores changes made by users to another table
I've got the tables all set up and the if statements, but I don't know the function to store current device, so I would be able to see which pc they used to make the change.
I have the function to store the current users and their id but not their device/computer id, or whatever would be the next best thing?
I have tried looking online but don't seem to find anything?
thank you very much in advance
Try using:
SYS_CONTEXT( 'USERENV', 'TERMINAL' )
It returns current user's OS ID.
You can read more about this function and it's other parameteres here:
https://docs.oracle.com
I have a very large number of rows in my table, table_1. Sometimes I just need to retrieve a particular row.
I assume, when I use SELECT query with WHERE clause, it loops through the very first row until it matches my requirement.
Is there any way to make the query jump to a particular row and then start from that row?
Example:
Suppose there are 50,000,000 rows and the id which I want to search for is 53750. What I need is: the search can start from 50000 so that it can save time for searching 49999 rows.
I don't know the exact term since I am not expert of SQL!
You need to create an index : http://dev.mysql.com/doc/refman/5.1/en/create-index.html
ALTER TABLE_1 ADD UNIQUE INDEX (ID);
The way I understand it, you want to select a row with id 53750. If you have a field named id you could do this:
SELECT * FROM table_1 WHERE id = 53750
Along with indexing the id field. That's the fastest way to do so. As far as I know.
ALTER table_1 ADD UNIQUE INDEX (<collumn>)
Would be a great first step if it has not been generated automatically. You can also use:
EXPLAIN <your query here>
To see which kind of query works best in this case. Note that if you want to change the where statement (anywhere in the future) but see a returning value in there it will be a good idea to put an index on that aswell.
Create an index on the column you want to do the SELECT on:
CREATE INDEX index_1 ON table_1 (id);
Then, select the row just like you would before.
But also, please read up on databases, database design and optimization. Your question is full of false assumptions. Don't just copy and paste our answers verbatim. Get educated!
There are several things to know about optimizing select queries like Range and Where clause Optimization, the documentation is pretty informative baout this issue, read the section: Optimizing SELECT Statements. Creating an index on the column you evaluate is very helpfull regarding performance too.
One possible solution You can create View then query from view. here is details of creating view and obtain data from view
http://www.w3schools.com/sql/sql_view.asp
now you just split that huge number of rows into many view (i. e row 1-10000 in one view then 10001-20000 another view )
then query from view.
I am pretty sure that any SQL database with a little respect for themselves does not start looping from the first row to get the desired row. But I am also not sure how they makes it work, so I can't give an exact answer.
You could check out what's in your WHERE-clause and how the table is indexed. Do you have a proper primary key? Like using a numeric data type for that. Do you have indexes on more columns, that is used in your queries?
There is also alot to concider when installing the database server, like where to put the data and log files, how much memory to give the server and setting the growth. There's a lot you can do to tune your server.
You could try and split your tables in partitions
More about alter tables to add partitions
Selecting from a specific partition
In your case you could create a partition on ID for every 50.000 rows and when you want to skip the first 50.000 you just select from partition 2. How to do this ies explained quite well in the MySQL documentation.
You may try simple as this one.
query = "SELECT * FROM tblname LIMIT 50000,0
i just tried it with phpmyadmin. WHERE the "50,000" is the starting row to look up.
EDIT :
But if i we're you i wouldn't use this one, because it will lapses the 1 - 49999 records to search.
I am new to MySQL partitioning, therefore any example will be appreciated.
I am trying to create a sort of an ageing mechanism for a data that is distributed between several MyISAM tables.
My question will actually include several sub-questions.
The relevant tables are:
First table contains raw data with high input frequency (next to each record there is an auto incremented id).
Second table contains processed results, there is a result record per every raw data record (result record contains the source id record of the auto incremented field of raw data record)
Questions:
I need to be able to partition the raw data table and result data table similarly so that both of them will include only 10 weeks of data in single partition (each raw data record contains unixtimestamp field), how do i do it , can someone write small example case for two such tables?.
I want to be able to change the 10 weeks constraint on the fly.
I want that when ever the current partition will be filled or a new partition is created , the previous (10 weeks before) partition will be deleted automatically.
I don't want the auto increment id integer to be overflown, as much as i understand the ids are unique for the partition only, so if i am not wrong the auto increment id will start from zero for the next partition? but what if the previous partition still exist, will i have 2 duplicated ids , how i know to reference only for the last id when i present a result record?
I want to load raw data using LOAD DATA INTO... instead of multiple inserts , is MySQL partitioning functionality affected?
And the last question, would you suggest some other approach to implement aging mechanism (i am writing Java implementation product that processes around 1 GB or raw data per day and stores the results in MySQL)
It's hard to give a real answer on this question since it depends on your data. But let me give you some things to think about.
I assume we're talking about some kind of logs with recent data (so not spanning multiple years). You can partition by range. You could add one field to your table with the year/week number (ie 201201, 201202, etc). If this question is related to your question about importing into multiple tables, you can easily do this is that import script.
On the fly as in, repartition your data on the fly (70GB?). I would not recommend it. But you could do it if you had the weeknumber in there. If you later want to change it to 12 days, you could add a column for the date and partition by that.
Well it won't be deleted automatically but a cron job can handle that right? Just check how many partitions there are, and if there are 3(?) delete the first one.
The partition needs to have a primary index on the field that you partition (if you want to use auto increment). Therefor you can never fully rely on the auto increment id alone. I don't see a way around this.
I'm not sure what you mean.
If your data is just some logs in chronological order then you might just use separate tables for each period. Then before you start the new period (at 00:00) check the last id of the last table, create a new table and set the auto increment to that value +1. Then your import will decide when a new period will begin so it can be easily changed. Your import script can use a small table in where it can store the next period.
LOAD DATA is really quite fast. I would just have two steps(in no partic order) - LOAD DATA and then 'delete .. where date < 10 weeks'. Autoincrement will go on for as long as the datatype you're using. If you wanted to be super careful you could push it back to zero periodically.
Once the data is in the 'raw' table run your routine to create the 'processed' table. We use a v similar process where I work. We keep a separate table that has 'write' and 'parse' pointers to all of our 'raw' tables. As new data comes in and gets parsed the appropriate row pointers get set. If the 'raw' table gets truncated you can reset the 'write' pointer but leave the 'parse' pointer. (we store the offset in another table when this happens - just to be sure).
And if I recommend , creating the index column for each of the related columns can also enhanced the performance Delete old data from multiple related tables since we have just compared the index numbers rather than strings.
I wonder if your tables are being sorted or not.
In the table tbl_dtdata I was created 7 partitions. I want to select the data from first partition p_APR. I was tried this query.SELECT COUNT(*) FROM tbl_dtdata PARTITION (p_Apr); But It is returning syntax error. Is there any other way to do this ?
Checkout following link that might be use full to you:
http://blog.sqlauthority.com/2008/01/25/sql-server-2005-database-table-partitioning-tutorial-how-to-horizontal-partition-database-table/
I have a resource that has a availability field that lists what hours of a day its available for use?
eg. res1 available between 0-8,19-23 hours on a day, the range here can be comma separated values of hour ranges. e.g are 0-23 for 24 hour access, 0-5,19-23 or 0-5,12-15,19-23
What's the best way to store this one? Is char a good option? When the resource is being accessed, my php needs to check the current hour with the hour defined here and then decide whether to allow this access or not. Can I ask mysql to tell me if the current hour is in the range specified here?
I'd store item availability in a separate table, where for each row I'd have (given your example):
id, startHour, endHour, resourceId
And I'd just use integers for the start and end times. You can then do queries against a join to see availability given a certain hour of the day using HOUR(NOW()) or what have you.
(On the other hand, I would've preferred a non-relational database like MongoDb for this kind of data)
1) create a table for resource availability, normalized.
CREATE TABLE res_avail
{
ra_resource_id int,
ra_start TIME,
ra_end TIME
# add appropriate keys for optimization here
)
2) populate with ($resource_id, '$start_time', '$end_time') for each range in your list (use explode())
3) then, you can query: (for example, PHP)
sql = "SELECT ra_resource_id FROM res_avail where ('$time' BETWEEN ra_start AND ra_end)";
....
I know this is an old question, but since v5.7 MySQL supports storing values in JSON format. This means you can store all ranges in one JSON field. This is great if you want to display opening times in your front-end using JavaScript. But it's not the best solution when you want to show all places that are currently open, because querying on a JSON field means a full table scan. But it would be okay if you only need to check on for one place at the time. For example, you load a page showing the details of one place and display whether it's open or closed.