I am making a mySQL table which lists ~70 products and information on whether they are compatible or not. For the sake of simplifying the question, I will pretend there were only four products.
Product1 Product2 Compatible?
A A Yes
A B No
A C Maybe
A D Yes
B A Yes
B B Yes
B C Yes
B D No
C A Yes
C B Maybe
C C Yes
C D Yes
D A Yes
D B No
D C Yes
D D Yes
If I already have a table like (every product is obviously compatible with itself)
Product1 Product2 Compatible?
A A Yes
B B Yes
C C Yes
D D Yes
Is there a way I can quickly fill out the first two columns so they follow the correct pattern? (so I dont have to be doing it manually)
One way to do this would be to use nested loops: If you know how many products you have, lets call it n products.
2^n total rows will be in your table. Additionally, product 1 will have each inventory item n times. (In your example 4 items, so 2^4 = 16 total rows and each item occurs in product1 column n=4 times.
Thus a nested loop can be achieved to do the insert...
$inventory = array(A, B, C, D);
for(i=0;i<2^n;i++){
for(j=0; j<n; j++){
//insert Column1=$inventory[i], Column2=$inventory[j];
}
}
Insert-After triggers!
And when inserting with phpMyadmin leave the column blank. let the trigger fill last column.
insert into compatibleProducts
select distinct p1.ProductID, p2.ProductID, 'Maybe'
from productTable p1
join productTable p2 on p1.ProductID <> p2.ProductID
I assumed that you already have them compatible with themselves, based on your second list.
Related
I am trying to find a simple solution to a Mysql problem. The problem is, I have 2 columns A and B, and in some rows I have data X and Y in these columns respectively. Now I have this data represented as below (only an example). The table may also have other data as presented below.
A | B
X | Y
X | Z
F | Y
X | Y
S | T
X | T
S | Y
Now I want to run a query which finds X and Y in their respective columns but shows them by priority. That is, columns where X and Y appear together should come up first and then the ones with individual columns.
Kindly note that there may be more columns and the data prioritization would apply accordingly.So more the columns match, more should be their priority while fetching results.
Data comparison is per field only.
I'm just exploring if this situation could be handled by Mysql or I have to look at something from PHP.
You can order by value, it should be st. like
... ORDER BY FIELD(A, 'X') DESC, FIELD(B, 'Y') DESC
You can use a "formula" to compute the weighs for your ordering:
SELECT A, B FROM TEST
ORDER BY CASE WHEN (A = 'X' AND B = 'Y') THEN 1 ELSE 0 END DESC
Check the example online: http://sqlfiddle.com/#!9/6545e4/8
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.
Apologies for the rubbish question title, but it's a bit tricky to summarise my requirement into a single line. I usually don't have an issue with MySQL JOINs but this one is throwing me.
I'm building a training feedback system and for one feature would like to display a list of all available workshops in the database, which workshops a given delegate has been assigned to and whether any feedback has been submitted by that delegate for those assigned workshops.
I could do this in a couple of queries, but I'm trying to do something a bit more elegant with a single query.
The pertinent details of my database structure:
WORKSHOPS table
id: INT
name: TINYTEXT
DELEGATES table
id: INT
name: TINYTEXT
FEEDBACK table
delegate_id: INT
workshop_id: INT
feedback: TEXT
DELEGATES_X_WORKSHOPS table
delegate_id: INT
workshop_id: INT
delegate_id and workshop_id in the tables are Foreign Keys to the DELEGATES and WORKSHOPS tables.
As any given delegate can be assigned to multiple workshops, I'm using the DELEGATES_X_WORKSHOPS table as a cross-referencing table so I can quickly search for who is assigned to any given workshop or which workshops any given delegate is assigned to.
However, I've tried LEFT JOINing a couple of different ways and I can't get a full list of workshops on the left and matches (if they exist) on the right for a given delegate_id.
Example data
Delegate Ross has delegate_id = 1
Registered workshops are
C++
PHP
ASP.NET
HTML5
JavaScript
Ross is assigned to PHP, HTML5 and JavaScript
Question 1 is this: how do I return the following for delegate_id=1:
[workshop] | [assigned]
C++ | null
PHP | TRUE
ASP.NET | null
HTML5 | TRUE
JavaScript | TRUE
(it doesn't matter right now what goes into column B, I just want a null if a particular delegate_id hasn't been assigned to a workshop).
I've used this:
SELECT
workshops.name,
delegates_x_workshops.delegate_id
FROM
workshops
LEFT JOIN
delegates_x_workshops
ON
workshops.id=delegates_x_workshops.workshop_id
WHERE
delegates_x_workshops.delegate_id=1
However I'm only returning the 3 rows where delegate_id=1, not 5 rows for all workshops.
Question 2 is a bit more involved:
Taking question 1 as a base, how would I work column C to display if feedback has been left for a workshop that Ross has been assigned to?
[workshop] | [assigned] | [givenfeedback]
C++ | null | null
PHP | TRUE | TRUE
ASP.NET | null | null
HTML5 | TRUE | null
JavaScript | TRUE | TRUE
Thanks in advance to anybody who makes it this far and has a clue what I'm blithering about. As I said, I could rattle through this with a few different queries, but I'm trying to keep things elegant.
No doubt half of this will need clarification, so ask any questions.
Thanks
For question 1, you need to move the where condition into the on clause. It is turning the left outer join into an inner join because non-matching rows have NULL values:
SELECT w.name, dxw.delegate_id
FROM workshops w LEFT JOIN
delegates_x_workshops dxw
ON w.id = dxw.workshop_id and
dxw.delegate_id = 1;
For the second question, I think this is what you want:
SELECT w.name,
(case when max(w.name = 'Ross') > 0 then 'True' end) as Assigned,
(case when count(f.workshop_id) > 0 then 'True' end) as Feedback
FROM workshops w LEFT JOIN
delegates_x_workshops dxw
ON w.id = dxw.workshop_id and
dxw.delegate_id = 1 LEFT JOIN
delegates d
on d.id = dxw.delegate_id LEFT JOIN
feedback f
on f.workshop_id = w.id
GROUP BY w.name;
For reference, here's my final query:
SELECT DISTINCT
workshops.id AS wid,
workshops.name AS workshop,
(delegates_x_workshops.delegate_id IS NOT NULL) AS assigned,
(initial_feedback.delegate_id IS NOT NULL
OR
ongoing_feedback.delegate_id IS NOT NULL) AS hasfeedback
FROM
workshops
LEFT JOIN
delegates_x_workshops
ON
workshops.id = delegates_x_workshops.workshop_id
AND
delegates_x_workshops.delegate_id = 1
LEFT JOIN
initial_feedback
ON
workshops.id = initial_feedback.workshop_id
AND
initial_feedback.delegate_id = 1
LEFT JOIN
ongoing_feedback
ON
workshops.id = ongoing_feedback.workshop_id
AND
ongoing_feedback.delegate_id = 1
ORDER BY
workshop ASC
For every workshop in the WORKSHOPS table, I'll get the id and name of the workshop, 1 or 0 if a given delegate_id is assigned and 1 or 0 if feedback of either type (I have 2 kinds) has been left for that workshop.
Scary to think that all I was missing was an AND condition on my LEFT JOIN.
Thanks again Gordon!
Relation 1 (r1):
ID | Name
1 John
2 Doe
3 Foo
Relation 2 (r2):
ID | Name
4 Johnny
5 Doey
6 Fooey
What will r1 theta join(r1.ID = r2.ID) r2 result in?
What will r1 cross r2 result in?
I'm just asking whether the resulting relations should change the names of the attributes to something else because there are 2 of each.
In relational algebra, product (cross join) is usually understood to be a special case of natural join where the joined relations happen to have no attributes in common. So it doesn't make sense to say A x B if A and B have common attributes. If A and B have attributes in common then A x B either means A ⋈ B or it means a mistake has been made and your DBMS or interpreter probably ought to report an error.
Theta join is a shorthand for natural join followed by a restriction. It must be preceded by a rename of some attribute(s) if the attributes in the theta expression would otherwise have the same names.
I have a watchlist system that I've coded, in the overview of the users' watchlist, they would see a list of records, however the list shows duplicates when in the database it only shows the exact, correct number.
I've tried GROUP BY watch.watch_id, GROUP BY rec.record_id, none of any types of group I've tried seems to remove duplicates. I'm not sure what I'm doing wrong.
SELECT watch.watch_date,
rec.street_number,
rec.street_name,
rec.city,
rec.state,
rec.country,
usr.username
FROM
(
watchlist watch
LEFT OUTER JOIN records rec ON rec.record_id = watch.record_id
LEFT OUTER JOIN members usr ON rec.user_id = usr.user_id
)
WHERE watch.user_id = 1
GROUP BY watch.watch_id
LIMIT 0, 25
The watchlist table looks like this:
+----------+---------+-----------+------------+
| watch_id | user_id | record_id | watch_date |
+----------+---------+-----------+------------+
| 13 | 1 | 22 | 1314038274 |
| 14 | 1 | 25 | 1314038995 |
+----------+---------+-----------+------------+
GROUP BY does not "remove duplicates". GROUP BY allows for aggregation. If all you want is to combine duplicated rows, use SELECT DISTINCT.
If you need to combine rows that are duplicate in some columns, use GROUP BY but you need to to specify what to do with the other columns. You can either omit them (by not listing them in the SELECT clause) or aggregate them (using functions like SUM, MIN, and AVG). For example:
SELECT watch.watch_id, COUNT(rec.street_number), MAX(watch.watch_date)
... GROUP by watch.watch_id
EDIT
The OP asked for some clarification.
Consider the "view" -- all the data put together by the FROMs and JOINs and the WHEREs -- call that V. There are two things you might want to do.
First, you might have completely duplicate rows that you wish to combine:
a b c
- - -
1 2 3
1 2 3
3 4 5
Then simply use DISTINCT
SELECT DISTINCT * FROM V;
a b c
- - -
1 2 3
3 4 5
Or, you might have partially duplicate rows that you wish to combine:
a b c
- - -
1 2 3
1 2 6
3 4 5
Those first two rows are "the same" in some sense, but clearly different in another sense (in particular, they would not be combined by SELECT DISTINCT). You have to decide how to combine them. You could discard column c as unimportant:
SELECT DISTINCT a,b FROM V;
a b
- -
1 2
3 4
Or you could perform some kind of aggregation on them. You could add them up:
SELECT a,b, SUM(c) "tot" FROM V GROUP BY a,b;
a b tot
- - ---
1 2 9
3 4 5
You could add pick the smallest value:
SELECT a,b, MIN(c) "first" FROM V GROUP BY a,b;
a b first
- - -----
1 2 3
3 4 5
Or you could take the mean (AVG), the standard deviation (STD), and any of a bunch of other functions that take a bunch of values for c and combine them into one.
What isn't really an option is just doing nothing. If you just list the ungrouped columns, the DBMS will either throw an error (Oracle does that -- the right choice, imo) or pick one value more or less at random (MySQL). But as Dr. Peart said, "When you choose not to decide, you still have made a choice."
While SELECT DISTINCT may indeed work in your case, it's important to note why what you have is not working.
You're selecting fields that are outside of the GROUP BY. Although MySQL allows this, the exact rows it returns for the non-GROUP BY fields is undefined.
If you wanted to do this with a GROUP BY try something more like the following:
SELECT watch.watch_date,
rec.street_number,
rec.street_name,
rec.city,
rec.state,
rec.country,
usr.username
FROM
(
watchlist watch
LEFT OUTER JOIN est8_records rec ON rec.record_id = watch.record_id
LEFT OUTER JOIN est8_members usr ON rec.user_id = usr.user_id
)
WHERE watch.watch_id IN (
SELECT watch_id FROM watch WHERE user_id = 1
GROUP BY watch.watch_id)
LIMIT 0, 25
I Would never recommend using SELECT DISTINCT, it's really slow on big datasets.
Try using things like EXISTS.
You are grouping by watch.watch_id and you have two results, which have different watch IDs, so naturally they would not be grouped.
Also, from the results displayed they have different records. That looks like a perfectly valid expected results. If you are trying to only select distinct values, then you don't want ot GROUP, but you want to select by distinct values.
SELECT DISTINCT()...
If you say your watchlist table is unique, then one (or both) of the other tables either (a) has duplicates, or (b) is not unique by the key you are using.
To suppress duplicates in your results, either use DISTINCT as #Laykes says, or try
GROUP BY watch.watch_date,
rec.street_number,
rec.street_name,
rec.city,
rec.state,
rec.country,
usr.username
It sort of sounds like you expect all 3 tables to be unique by their keys, though. If that is the case, you are simply masking some other problem with your SQL by trying to retrieve distinct values.