I have looked at other questions/answer regarding my question, but for some reason, every time I try to implement an answer exactly how they implemented it, it throws an error. But I am paginating some things now, and I need to order my results by column in another table.
Here is the code I have now:
SELECT `id`,`name`,`players`,`max_players`,`status`,`host`,`port`
FROM `servers`
LIMIT :to,:from
The table it is getting stuff from is the servers table, and it needs to get the column rank from the server_profiles table, and order it by that. I try to understand how MySQL joins work, but they always seem to confuse me, from looking at examples, to reading the markup on the MySQL wiki.
You can use join for that. For that you need to have a relation between both tables. I have used server.ID = server_profiles.serversID for example.
SELECT s.* FROM servers s
JOIN server_profiles sp
ON s.ID = sp.serversID
ORDER BY sp.rank
LIMIT :to,:from
See this SQLFiddle
Related
I have PHP system that runs a MYSQL query like below
select
order.id,
order.name,
order.date,
customer.name,
items.coupon_code,
from order
left join customer on order.custid = customer.id
left join items on items.coupon_code = order.coupon_code
where items.coupon_new_code is null
and order.status = 1000
AND order.promo_code in (1,2)
order table has 800K records and items table has 300k records. When I run this the query takes about 9 hours to finish!
If I comment the left join to the items table then the query runs in a few seconds! I am not very efficient with MySQL joins and would really really appreciate if someone can tell me how I can optimise this query to run in an acceptable time frame.
Try changing
LEFT JOIN to INNER JOIN (or just JOIN)
This will work to speed things up assuming that you only want to see orders that have both customers and items associated with them. Currently your query is trying to return all data from the order table but that's not needed. It's possible other changes to the database structure could improve things as well.
The top answer here provides a useful diagram that demonstrates the difference between these types of statements.
At the very least you need an index on coupon_code on both order and items tables. Consider also adding to a compound index, the other field you are joining on custid, as well as on your WHERE conditions items.coupon_new_code, order.status and order.promo_code. Knowing next to nothing about your data I can only speculate about what the dbms will use. Try various combinations in a compound key and run explain to see what's being used. It's really going to depend on the specificity of the data in your columns.
Posting the output of EXPLAIN along with the tables' schema will help us improve these answers.
I have a table topics. And I have two queries which select different data, one for the table votings and one from the table messages. topics has a field m_group which is a foreign key for messages. This field can either be NULL or a group for entries in messages (group is a field in this table). If this field is set to a group, it should perform query 1 to select all messages or if it is not set it should perform query 2 to select all votings for this specific topic. I'm using Postgres and PHP on an Apache Webserver.
Now my question is what is the recommended way to go. I came up with two solutions (not sure if solution 2 is actually possible, haven't tried it yet).
Solution 1
First select the field m_group. Then determine if it is set via PHP and perform the associated query.
Solution 2
Use a IF THEN ELSE statement
Basically the query should then look something like this
IF t.m_group IS NULL
THEN
query2
ELSE
query1
As already mentioned, I'm not sure if solution 2 is possible. What would be the best way to handle this? Solution 1 performs two queries, I think this is inefficient.
UPDATE
As mentioned above, it should perform the queries for a specific topic. You have the id of this topic. How can you specify this in solution 2? And does the IF THEN ELSE statement already know the alias t for topics, if that is specified in the queries?
If I understand you right, you need to use two subqueries as sets of data, while you should use one of them as a source depending on what's in the m_group field. Your second approach is good if you only select a few rows. However, if you need to grab a lot of data from the table, this way you will need to perform too many subqueries. I would rather first grab all the data you need from topics and then select what you need with both queries.
Pseudo SQL query will look like that:
with t1 as (select t.id, group_m, ... from topics t where t.m_group is not null),
t2 as (select t.id, ... from topics t where t.m_group is null)
select id, title, SUM(subtable_id) AS votes
from query1
join t1 on t1.id = query1.id and...
union
select id, title, SUM(subtable_id) AS votes
from query2
join t2 on t2.id = query2.id and...
I am trying to query two tables: finished_events and flagged_events. 1st of all I need everything related to the company_id so
SELECT *
FROM finished_events
WHERE company_id=$id
ORDER by schedule, timestamp
I then changed this to:
SELECT * FROM finished_events
INNER JOIN flagged_events
ON finished_events.company_id=flagged_events.company_id
WHERE finished_events.company_id=$id
ORDER by finished_events.schedule, finished_events.timestamp
I have tried using FULL JOIN, LEFT JOIN, and RIGHT JOINs all unsuccessful. Specifically what I want is to get is a combined effort of the following code:
$sql = "SELECT *
FROM finished_events
WHERE company_id=$id
ORDER by schedule, time_stamp";
$flagged_sql = "SELECT *
FROM flagged_events
WHERE company_id=$id
ORDER by schedule, time_stamp";
The tables are a bit different so UNION won't work here. I can post dummy database entries but this won't be of too much help as I need all from both tables. The 2 links between the tables would be the company_id and the schedule columns. Essentially what is going on behind the scenes is timestamps being put into a different table to which I then process either into finished_events or flagged_events. Flagged events will need the user to do something about it until it is a finished event. So this script is generating the data for the GUI, hence why I need to query both tables and create an associative array of customer details then an array of events (from these 2 tables). So creating the assoc_array is no problem I just need to get this query to spit out all the events and order them correctly. Let me know if you need anything specific to solve this one, thanks :)
EDIT
SQL Fiddle: http://sqlfiddle.com/#!2/d4c30/1
this almost fixes it but not quite right, it repeats entries at the bottom
If I understood correctly, this may be useful for you:
SELECT a.* FROM (
SELECT *, 'finished' as event_type FROM finished_events
UNION
SELECT *, 'flagged' as event_type FROM flagged_events) a
ORDER BY a.schedule, a.time_stamp
I hate to submit a new question, but everyone else has some slight thing that is different enough to make this one seem necessary to ask.
Users are to type in a vendor name, and then see all the "kinds" of things they have bought from that company, in a list, sorted by the lowest-inventory-on-hand.
Summary:
I have three tables.
There are more fields than these, but these are the relevant ones (as far as I can tell).
stuff_table
stuff_vendor_name *(search this field with $user_input, but only one result per lookup_type)*
lookup_type
lookup_table
lookup_type
lookup_quantity (order by this)
category_type
category_table
category_type
category_location (check if this field == $this_location, which is already assigned)
Wordier Explanation:
The users are searching for a value that is contained only in the stuff_table -- distinct stuff_vendor_name values for each lookup_type. Each item can be bought from multiple sources, the idea is to see if any vendor has ever sold even one of any type of item before.
But the results need to be ORDER BY the lookup_quantity, in the lookup_table.
And importantly, I have to check to see if they are searching the correct location for these categories, located in the category_table in the category_location field.
How do I efficiently make this query?
Above, I mentioned the variables that I have:
$user_input (the value we are searching for distinct matches in the stuff_vendor_name field) and $current_location.
To understand the relationship of these tables, I will use an example.
The stuff_table would have dozens of entries with dozens of vendors, but have a lookup_type of, say, "watermelon," "apple," or "cherry."
The lookup_table would give the category_type of "Jellybean." One category type can have multiple lookup_types. But each lookup_type has exactly one category_type.
You are not sharing much about the relationships, but try this:
SELECT *
FROM stuff_table st
LEFT JOIN lookup_table lt
ON st.lookup_type = lt.lookup_type
LEFT JOIN category_table ct
ON lt.category_type = ct.category_type
AND ct.category_location = $this_location
GROUP BY st.lookup_type
ORDER BY lt.lookup_quantity
WHERE st.stuff_vendor_name = $user_input
From a first glance at it you could use foreign keys in your tables to make link between them or using the LEFT JOIN mysql command to make abstraction of another linked table.
The only example I can think of is on a Doctrine pattern, but I think you'll get what I'm saying:
$q = Doctrine_Query::create()
->from('Default_Model_DbTable_StuffTable s')
->leftJoin('s.LookupTable l')
->leftJoin('s.CategoryTable c')
->orderBy('l.lookup_quantity DESC');
$stuff= $q->execute(array(), Doctrine_Core::HYDRATE_ARRAY);
I made a nested query instead.
The final code looks like this:
$query_row=mysql_query(
"SELECT DISTINCT * FROM table_a WHERE
field_1 IN (SELECT field_1 FROM table_b WHERE field_2 = $field_2)
AND field_3 IN (SELECT field_3 FROM table_c WHERE field_4 = $field_4)
ORDER BY field_5 DESC
");
This was incredibly simple. I just didn't know you could do a nested query like that.
I read it was "bad form" because it makes some kind of search optimization not as good as it could be, so be careful using nested select statements.
However for me, it seemed to actually be significantly faster.
So I've got a little forum I'm trying to get data for, there are 4 tables, forum, forum_posts, forum_threads and users. What i'm trying to do is to get the latest post for each forum and giving the user a sneak peek of that post, i want to get the number of posts and number of threads in each forum aswell. Also, i want to do this in one query. So here's what i came up with:
SELECT lfx_forum_posts.*, lfx_forum.*, COUNT(lfx_forum_posts.pid) as posts_count,
lfx_users.username,
lfx_users.uid,
lfx_forum_threads.tid, lfx_forum_threads.parent_forum as t_parent,
lfx_forum_threads.text as t_text, COUNT(lfx_forum_threads.tid) as thread_count
FROM
lfx_forum
LEFT JOIN
(lfx_forum_threads
INNER JOIN
(lfx_forum_posts
INNER JOIN lfx_users
ON lfx_users.uid = lfx_forum_posts.author)
ON lfx_forum_threads.tid = lfx_forum_posts.parent_thread AND lfx_forum_posts.pid =
(SELECT MAX(lfx_forum_posts.pid)
FROM lfx_forum_posts
WHERE lfx_forum_posts.parent_forum = lfx_forum.fid
GROUP BY lfx_forum_posts.parent_forum)
)
ON lfx_forum.fid = lfx_forum_posts.parent_forum
GROUP BY lfx_forum.fid
ORDER BY lfx_forum.fid ASC
This get the latest post in each forum and gives me a sneakpeek of it, the problem is that
lfx_forum_posts.pid =
(SELECT MAX(lfx_forum_posts.pid)
FROM lfx_forum_posts
WHERE lfx_forum_posts.parent_forum = lfx_forum.fid
GROUP BY lfx_forum_posts.parent_forum)
Makes my COUNT(lfx_forum_posts.pid) go to one (aswell as the COUNT(lfx_forum_threads.tid) which isn't how i would like it to work. My question is: is there some somewhat easy way to make it show the correct number and at the same time fetch the correct post info (the latest one that is)?
If something is unclear please tell and i'll try to explain my issue further, it's my first time posting something here.
Hard to get an overview of the structure of your tables with only one big query like that.
Have you considered making a view to make it easier and faster to run the query?
Why do you have to keep it in one query? Personally I find that you can often gain both performance and code-readability by splitting overly complicated queries into more parts.
But hard to get an overview so can't really give a good answer to your question:)
Just add num_posts column to your table. Don't count posts with COUNT().
Can we get some...
Show Tables;
Desc Table lfx_forum_posts;
Desc Table lfx_forum_threads;
Desc Table lfx_forum_users;
Desc Table lfx_forum;
Here's some pseudo code
select f.*, (select count(*) from forum_posts fp where fp.forum_id = f.id) as num_posts,
(select count(*) from forum_threads ft where ft.forum_id = f.id) as num_threads,
(select max(fp.id) from forum_posts fp
where fp.id = f.id
) as latest_post_id,
from forums f;
Then go on to use latest_post_id in a seperate query to get it's information.
if it doesn't like using f before it's declared then make a temporary table for this then you update every time the query is ran.