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MYSQL Group together query

Hi Everyone,

I am trying to put together a query that does the following:

I have a table with 512 entries in it (initially, this will increase with records at we add to it)

This table has columns id, ip_address, in_use where (id is auto_incrementing and primary) and in_use is bool true / false.

Basically I have a list of addresses in this (like I said initially it's got 512)

I need to ask mysql to return rows not in use, but group them together by a set number (ie I need 11 free addresses),

However, this system will have rows marked false on the in_use col right next to others with true.

I need a way to grab a set amount of IP's the id being broken sequentially... example

ids => in_use

1 => false

2 => false

3 => false

4 => false

5 => false

6 => false

7 => false

8 => false

9 => true

10 => true

11 => false

12 => false

13 => false

14 => false

15 => false

16 => false

17 => false

18 => false

19 => false

20 => false

21 => false

22 => false

23 => false

Now if I query for 11 free addresses, closest to the top, it will bring back the list of id's 1 to 12 skipping over 9, this won't work for what I am trying to do :(

What I would like it to do is realize that 9 is in use so cannot use that, thus cannot make a sequential group and pick from 11 to 22... as that is the next available sequential set.

Is there any way to structure a query for this? Is it even possible in MySQL?

Your help is kindly appreciated, Karl.

Aaron Tomosky

Without a fully flushed out solution I think I can say it may be possible and get you started.
If you add a rowcount column to the query output and then take the last part of the ip and subtract the rownumber, that should give you a constant number for contiguous ip addresses. Group by that column and add a count to see contiguous blocks. Change the ip to max(ip), ad a min(ip) and you should get start and end and counts of all the blocks. I won't be back at a PC until tomorrow to test all this but I think I will work and someone may be able to write it up before then ifyou can't figure it out.

crucial_paradigm

ASKER

Thanks Aaron!

I hope to see some type of demonstration of this soon, I am a bit baffled by your terminology so I will await your thoughts

I am doing this currently in the application level, but practically dropping a few thousand rows into array returns is not a good idea....

I look forward to hearing from you!
--Karl.

SOLUTION

Aaron Tomosky

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Sharath S

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kristinalim

If you'll be getting more queries than updates, you might want to consider a caching mechanism:

1. Add column for tracking number of not in use IP addresses from current record until the next IP address not in use. For example:

id  in_use  contiguous_unused
1   true      1
2   false     0
3   true      1
4   true      2
5   false     0

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2. Then, when marking a record with ID x not in use:

# Get first used IP address after current record with ID x.
next_used_id : SELECT MIN(id) FROM ip_addresses WHERE in_use IS TRUE AND id > x;
# Get contiguous_unused for current record.
current_contiguous_unused : SELECT COUNT(*) + 1 FROM ip_addresses WHERE in_use IS FALSE and id > x and id < next_used_id;
# Set contiguous_unused of current record.
UPDATE ip_addresses SET contiguous_unused = current_contiguous_unused WHERE id = x;
# Get last used IP address before current record with ID x.
last_used_id : SELECT MAX(id) FROM ip_addresses WHERE in_use IS TRUE AND id < x;
# Increment contiguous_unused by current_contiguous_unused for all records after last_used_id until previous record.
UPDATE ip_addresses SET contiguous_unused = contiguous_unused + current_contiguous_unused WHERE id > last_used_id AND id < x;

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Essentially, you would be adjusting the cached count for records with affected counts.

3. When marking a record with ID x as in use:

# Get last used IP address before current record with ID x.
last_used_id : SELECT MAX(id) FROM ip_addresses WHERE in_use IS TRUE AND id < x;
# Set contiguous_unused of current record.
UPDATE ip_addresses SET contiguous_unused = 0 WHERE id = x;
# Decrement contiguous_unused by 1 for all records after last_used_id until previous record.
UPDATE ip_addresses SET contiguous_unused = contiguous_unused - 1 WHERE id > last_used_id AND id < x;

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4. A new record will just have 0 for contiguous_unused if in_use and 1 otherwise.
5. Selecting first set of 11 contiguous records:

SELECT MIN(id) FROM ip_addresses WHERE contiguous_unused > 11;

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This is a rough algorithm. Of course you will have to catch cases when last used or next used record is not existent (start or end of table) and optimize for mass inserts/updates.

Just a possibility.

kristinalim

Correction

5. Selecting first set of 11 contiguous records:

SELECT MIN(id) FROM ip_addresses WHERE contiguous_unused >= 11;

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You can have flexible queries with this too, if you want to get the smallest unused range or even middle depending on your method for space optimization.

crucial_paradigm

ASKER

Thank you all for your replies,

Because of this I have now been able to form my database table and use it correctly!

--Karl