I have a set of database tables named like:
site_1_details
site_2_details
site_3_details
...
site_420_details
all tables have the same fields, like:
ID | SETTING | VALUE
----------------------
1 name Site 1 Name
2 desc Site 1 Desc
3 email Site 1 Email...
...
(only the value fields are different)
How can I get a set of values from certain tables?
For example, I want to get the name & email values from sites 3,7 and 15. How could I do that with a SQL query?
SELECT 3 AS siteID, name, email
FROM site_3_details
UNION
SELECT 7 AS siteID, name, email
FROM site_7_details
UNION
SELECT 15 AS siteID, name,email
FROM site_15_details
This is a horribly bad design. Why couldn't you put a "siteID" field into a single table, which'd reduce the query to:
SELECT name, email
FROM site_details
WHERE siteID IN (3,7,15);
comment followup:
Ah well, then you just modify the individual queries:
SELECT 7 AS siteID, ID as fieldID, name AS fieldName
FROM site_7_details WHERE SETTING IN ('name', 'email')
UNION
....
Any reason you've designed the tables like this? Sounds like you're trying to implement your own database on TOP of a database engine which is already perfectly suited to doing this kind of relational data handling.
Related
I have three separate tables that represent student attendance for three weeks, respectively. I want to be able to generate four columns that break down the attendance by week for each of the students. If a student was present multiple times a week, the number of times present should be added. Also, if a student was present in one week and not the next, it would get 1 for the month present (assuming it was only present once) and and 0 for the one absent. I have tried to multiple variations of count() and joins but to no avail. Any help would be greatly appreciated. The following is a truncated fiddle:
http://www.sqlfiddle.com/#!9/b847a
Here is a sample of what I am trying to achive:
Name | CurrWeek | LastWeek | TwoWkAgo
Paula | 0 | 2 | 3
Rather than three tables you should have only one with a column for the week. So naturally one solution for your request is to build it on-the-fly with UNION ALL:
select
name,
sum(week = 'currentWeek') as currentWeek,
sum(week = 'lastWeek') as lastWeek,
sum(week = 'thirdWeek') as thirdWeek
from
(
select 'currentWeek' as week, name from currentWeek
union all
select 'lastWeek' as week, name from lastWeek
union all
select 'thirdWeek' as week, name from thirdWeek
) all_weeks
group by name
order by name;
(If you want to join the three tables instead, you'd need full outer joins, which MySQL does not support, if I remember correctly. Anyway, my advice is to change the data model.)
You can try this query:
select currweek.name, currweek.att, lastweek.att, twoWkAgo.att from
(select name, count(attendance) as att from currentWeekTable group by name) currweek,
(select name, count(attendance) as att from lastWeekTable group by name) lastweek,
(select name, count(attendance) as att from twoWeekTable group by name) twoWkAgo
where twoWkAgo.name=currWeek.name and twoWkAgo.name=lastweek.name;
Assuming your 3 attendance tables contain name as common field.
I have the following situation. I have a table with all info of article. I will like to compare the same column with it self. because I have multiple type of article. Single product and Master product. the only way that I have to differences it, is by SKU. for example.
ID | SKU
1 | 11111
2 | 11112
3 | 11113
4 | 11113-5
5 | 11113-8
6 | 11114
7 | 11115
8 | 11115-1-W
9 | 11115-2
10 | 11116
I only want to list or / and count only the sku that are full unique. follow th example the sku that are unique and no have variant are (ID = 1, 2, 6 and 10) I will want to create a query where if 11113 are again on the column not cout it. so in total I will be 4 unique sku and not "6 (on total)". Please let me know. if this are possible.
Assuming the length of master SKUs are 5 characters, try this:
select a.*
from mytable a
left join mytable b on b.sku like concat(a.sku, '%')
where length(a.sku) = 5
and b.sku is null
This query joins master SKUs to child ones, but filters out successful joins - leaving only solitary master SKUs.
You can do this by grouping and counting the unique rows.
First, we will need to take your table and add a new column, MasterSKU. This will be the first five characters of the SKU column. Once we have the MasterSKU, we can then GROUP BY it. This will bundle together all of the rows having the same MasterSKU. Once we are grouping we get access to aggregate functions like COUNT(). We will use that function to count the number of rows for each MasterSKU. Then, we will filter out any rows that have a COUNT() over 1. That will leave you with only the unique rows remaining.
Take that unique list and LEFT JOIN it back into your original table to grab the IDs.
SELECT ID, A.MasterSKU
FROM (
SELECT
MasterSKU = SUBSTRING(SKU,1,5),
MasterSKUCount = COUNT(*)
FROM MyTable
GROUP BY SUBSTRING(SKU,1,5)
HAVING COUNT(*) = 1
) AS A
LEFT JOIN (
SELECT
ID,
MasterSKU = SUBSTRING(SKU,1,5)
FROM MyTable
) AS B
ON A.MasterSKU = B.MasterSKU
Now one thing I noticed from you example. The original SKU column really looks like three columns in one. We have multiple values being joined with hypens.
11115-1-W
There may be a reason for it, but most likely this violates first normal form and will make the database hard to query. It's part of the reason why such a complicated query is needed. If the SKU column really represents multiple things then we may want to consider breaking it out into MasterSKU, Version, and Color or whatever each hyphen represents.
I have a system with products. Everytime a user enters a product, I insert a record into my database.
I have a table with users and id_products, like this:
users id_product
____________________________
jondoe 2
george 9
jondoe 5
jondoe 2
george 9
george 9
george 2
I need a result (query) wich shows what is TOP visited product id for each user, so the result would be something like this:
jondoes most visited product is ID 2
georges most visitedproduct is ID 9
I was looking for the answer but I am not able to figure it out. Thanks a lot for your help, I appreciate it a lot.
Jan
This is a pain because it involves aggregation. One way to solve this uses a very complicated query. Another uses variables. A third method uses an aggregation trick that works under many circumstances:
select user,
substring_index(group_concat(id_product order by cnt desc), ',', 1) as mostCommonProduct
from (select user, id_product, count(*) as cnt
from t
group by user, id_product
) t
group by user;
One danger when using this method is that the intermediate result might be too long. You can set the group_concat_max_len system variable to get around that particular problem.
I've got a table where the columns that matter look like this:
username
source
description
My goal is to get the 10 most recent records where a user/source combination is unique. From the following data:
1 katie facebook loved it!
2 katie facebook it could have been better.
3 tom twitter less then 140
4 katie twitter Wowzers!
The query should return records 2,3 and 4 (assume higher IDs are more recent - the actual table uses a timestamp column).
My current solution 'works' but requires 1 select to generate the 10 records, then 1 select to get the proper description per row (so 11 selects to generate 10 records) ... I have to imagine there's a better way to go. That solution is:
SELECT max(id) as MAX_ID, username, source, topic
FROM events
GROUP BY source, username
ORDER BY MAX_ID desc;
It returns the proper ids, but the wrong descriptions so I can then select the proper descriptions by the record ID.
Untested, but you should be able to handle this with a join:
SELECT
fullEvent.id,
fullEvent.username,
fullEvent.source,
fullEvent.topic
FROM
events fullEvent JOIN
(
SELECT max(id) as MAX_ID, username, source
FROM events
GROUP BY source, username
) maxEvent ON maxEvent.MAX_ID = fullEvent.id
ORDER BY fullEvent.id desc;
Firstly I'd like to start by apologizing for the potentially miss-leading title... I am finding it difficult to describe what I am trying to do here.
With the current project I'm working on, we have setup a 'dynamic' database structure with MySQL that looks something like this.
item_details ( Describes the item_data )
fieldID | fieldValue | fieldCaption
1 | addr1 | Address Line 1
2 | country | Country
item_data
itemID | fieldID | fieldValue
12345 | 1 | Some Random Address
12345 | 2 | United Kingdom
So as you can see, if for example I wanted to lookup the address for the item 12345 I would simply do the statement.
SELECT fieldValue FROM item_data WHERE fieldID=1 and itemID=12345;
But here is where I am stuck... the database is relatively large with around ~80k rows and I am trying to create a set of search functions within PHP.
I would like to be able to perform a query on the result set of a query as quickly as possible...
For example, Search an address name within a certain country... ie: Search for the fieldValue of the results with the same itemID's as the results from the query:
'SELECT itemID from item_data WHERE fieldID=2 and fieldValue='United Kingdom'..
Sorry If I am unclear, I have been struggling with this for the past couple of days...
Cheers
You can do this in a couple of ways. One is to use multiple joins to the item_data table with the fieldID limited to whatever it is you want to get.
SELECT *
FROM
Item i
INNER JOIN item_data country
ON i.itemID = country.itemID
and fieldid = 2
INNER JOIN item_data address
ON i.itemID = country.itemID
and fieldid = 1
WHERE
country.fieldValue= 'United Kingdom'
and address.fieldValue= 'Whatever'
As an aside this structure is often referred to as an Entry Attribute Value or EAV database
Sorry in advance if this sounds patronizing, but (as you suggested) I'm not quite clear what you are asking for.
If you are looking for one query to do the whole thing, you could simply nest them. For your example, pretend there is a table named CACHED with the results of your UK query, and write the query you want against that, but replace CACHED with your UK query.
If the idea is that you have ALREADY done this UK query and want to (re-)use its results, you could save the results to a table in the DB (which may not be practical if there are a large number of queries executed), or save the list of IDs as text and paste that into the subsequent query (...WHERE ID in (...) ... ), which might be OK if your 'cached' query gives you a manageable fraction of the original table.