I would like to store random numbers in one MySql table, randomly retrieve one and insert it into another table column each time a new record is created. I want to delete the retrieved number from the random number table as it is used.
The random numbers are 3 digit, there are 900 of them.
I have read several posts here that describe the problems using unique random numbers and triggering their insertion. I want to use this method as it seems to be reliable while generating few problems.
Can anyone here give me an example of a sql query that will accomplish the above? (If sql query is not the recommended way to do this please feel free to recommend a better method.)
Thank you for any help you can give.
I put together the two suggestions here and tried this trigger and query:
CREATE TRIGGER rand_num before
INSERT ON uau3h_users FOR EACH ROW
insert into uau3h_users (member_number)
select random_number from uau3h_rand900
where random_number not in (select member_number from uau3h_users)
order by random_number
limit 1
But it seems that there is already a trigger attached to that table so the new one cause a conflict, things stopped working until I removed it. Any ideas about how accomplish the same using another method?
You are only dealing with 900 records, so performance is not a major issue.
If you are doing a single insert into a table, you can do something like the following:
insert into t(rand)
select rand
from rand900
where rand not in (select rand from t)
order by rand()
limit 1
In other words, you don't have to continually delete from one table and move to the other. You can just choose to insert values that don't already exist. If performance is a concern, then indexes will help in this case.
More than likely you need to take a look into Triggers. You can do some stuff for instance after inserting a record in a table. Refer this link to more details.
http://dev.mysql.com/doc/refman/5.0/en/create-trigger.html
Related
Example tables (not actual database):
In this example, I would have the SecurityCode(Unique), and Time. My current solution involves attempting to add a new Person using the security code, then querying the ID, then adding to the Times table. This is 3 separate statements and could likely be a lot faster. Any advice on how to optimise this?
Thanks.
Edit: I previously forgot to mention that this is normally done in a batch of 30-40 records.
I am also considering using SecurityCode as the foreign key in Times.
I think there are many ways of achieve this, the easiest:
Try using "IF", you only need it for the first step of your statement, the last two are independent to the result of this evaluation.
Plus, save your security code in a variable, then you will save one table scan (you already have it)
**please note its just pseudo-code**
IF (exists select * from person where securityCode = #securityCode) then
Step 1
End
Step 2
Step 3
Can you try it?
The fastest way seemed to be to batch ignore insert all security codes, then batch insert all Times with a subquery to select the correct ID from Person.
I have to use this for a project at work, and am running into some trouble. I have a large database (58mil rows) that I have figured out how to query down to what I want and then write this row in to a separate table. Here is my code so far:
insert into emissionfactors(pollutantID,fuelTypeID,sourceTypeID,emissionFactor)
select pollutantID,fuelTypeID,sourceTypeID,avg(ratePerDistance) as emissionFactor
from onroad_run_1.rateperdistance
where pollutantID=45
and fuelTypeID=2
and sourceTypeID=32;
I have about 60 different pollutant ID's, and currently I am manually changing the pollutantID number on line 5 and executing the script to write the row into my 'emissionfactors' table. Each run takes 45 seconds and I have several other fuel types and source types to do so this could take like 8 hours of clicking every 45 seconds. I have some training in matlab and thought I could put a while loop around the above code, create an index, and have it loop through from 1 to 184 on the pollutant IDs but I can't seem to get it to work.
Here are my goals:
- loop the pollutantID from 1 to 184.
-- not all integers are in this range, so need it to simply add one to the index and check to see if that number is found in the pollutantID column if the index is not found.
-- if the index number is found in the pollutant ID column, execute my above code to write the data into my other table
You do not need a while loop, all you need is to change your where clause to use a BETWEEN clause and also tell it what you want to base the average on by adding a GROUP BY clause
insert into emissionfactors(pollutantID,fuelTypeID,sourceTypeID,emissionFactor)
select pollutantID,fuelTypeID,sourceTypeID,avg(ratePerDistance) as emissionFactor
from onroad_run_1.rateperdistance
where pollutantID BETWEEN 1 AND 184
and fuelTypeID=2
and sourceTypeID=32
GROUP BY pollutantID , fuelTypeID, sourceTypeID;
If in fact you want the entire range of the pollutantID, fuelTypeID and sourceTypeID that exists you can just remove the where clause altogether.
insert into emissionfactors(pollutantID,fuelTypeID,sourceTypeID,emissionFactor)
select pollutantID,fuelTypeID,sourceTypeID,avg(ratePerDistance) as emissionFactor
from onroad_run_1.rateperdistance
GROUP BY pollutantID , fuelTypeID, sourceTypeID;
You also don't need to check if the row exists before executing the query, as if it doesn't exist and returns no rows it just won't insert any.
As to the speed issue, you will need to look at adding some table indexes to your table to improve performance. In this case an index that has pollutantID, fuelTypeID and sourceTypeID would speed things up greatly.
My advice, ask for help at work. It is better to admit early that you do not know how to do something and get proper help, as you also mention that you have different fuel types that you want, but the details of that are missing from your question.
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've been using MySQL at work, but I'm still a bit of a noob at more advanced queries, and often find myself writing lengthy queries that I feel (or hope) could be significantly shortened.
I recently ran into a situation where I need to create X number of new entries in a table for each entry in another table. I also need to copy a value from each row in the second table into each row I'm inserting into the first.
To be clear, here's pseudocode for what I'm attempting to do:
For each row in APPS
create new row in TOKENS
set (CURRENT)TOKENS.APP_ID = (CURRENT)APPS.APP_ID
Any help is appreciated, even if it boils down to "this isn't possible."
As a note, the tables only share this one field, and I'll be setting other fields statically or via other methods, so simply copying isn't really an option.
You don't need a loop, you can use a single INSERT command to insert all rows at once:
INSERT INTO TOKENS (APP_ID)
SELECT APP_ID
FROM APPS;
If you want to set other values for that row, simply modify the INSERT list and SELECT clause. For example:
INSERT INTO TOKENS (APP_ID, static_value, calculated_value)
SELECT APP_ID, 'something', 'calculated-' + APP_ID
FROM APPS
I want to store some records in mysql database. records have a date column. i want to store them in sorting order of that date column.
For example, record having date 27/sep/2011 get stored as first row on the top of record having date 26/sep/2011 as:
id_1,name_1,27/sep/2011
id_2,name_2,26/sep/2011
if new records come on future dates they would get inserted on the top.
I DONT want to order them while using select by using order by desc .
i want they get inserted into db directly in sorted order.
how to do this???
thanks...
I am always surprised when people want to determine physical order of storing records.
Basically, it's a terrible idea for multiple reasons.
1) How the record is physically stored should not be of your concern.
2) How the record is presented should be of your concern. That's why we have ORDER BY built in.
3) Determining physical storage should be done by experts in the field, since it has performance implications - which is a topic in its own and I won't go into details.
Basically, worry about getting the data out in the sorted order, not getting it in in the sorted order.
Reason why it's a bad idea is because you'll be tampering with the primary key which is never, ever a good idea. On top of that, you'll have to reorder the records every time you insert something. Just don't reinvent hot water.
You could do this by adding another table - inserting all of the records into that table (the current and the new ones) then doing and insert as follows :
INSERT into newtable
select * from temptable
order by temptable.date
Why do you need to do this ? why not just use orderby on the query ?
As pointed out in the comments below - you would need to truncate the newtable each time
You cannot choose where to insert your row.
Here's one possible solution: MySQL syntax for inserting a new row in middle rows?