I've got three tables in a MySql database that I'm joining in a query to get id/value pairs.
| A | B | C |
| -------- |--------------|---------------|
| id | id | id |
| name | fooId | attributeId |
| desc | value | displayIndex |
| ... | attributeId | ... |
What I have now is:
SELECT C.id, B.value
FROM A, B, C
WHERE A.id = B.attributeId
AND A.id = C.attributeId
AND B.fooId = 25
ORDER BY C.displayIndex
So basically we're joining B and C through A. It used to be that an entry in the C table had to have a corresponding (parent) entry in the A table. However, that will no longer be the case. The C table will still be MOSTLY controlled by the A table, however, there are some instances when we need a stand alone (always on) entry in the C table.
EDIT
I want all the records from B and C that match on attributeId but I also want any record where C.attributeId = -1. Can someone help with what I'd need to do with this query?
Edit #2
Based on feedback and suggestions you guys have made and some googling I now have this:
(SELECT C.id, B.value, C.displayIndex
FROM B, C
WHERE B.attributeId = C.attributeId
AND B.fooId = 25)
UNION
(SELECT C.id, null, C.displayIndex
FROM C
WHERE C.attributeId = -1)
ORDER BY 3
Is there a better what to do this? Are there any problems with UNION?
I've updated my answer to address the edits from the OP.
This will return all records where the attributeId for tables B and C match,
with B.fooId = 25, OR C.attributeId = -1.
When C.attributeId = -1 and there is no match in table B, NULL will be returned in place of B.Value, which appears to be acceptable based on the Edit #2 from the OP
SELECT C.Id, B.Value, C.displayIndex
FROM C
LEFT JOIN B ON C.attributeId = B.attributeId
WHERE B.fooId = 25
OR C.attributeId = -1
ORDER BY C.DisplayIndex ASC
You're probably getting a Cartesian product.
Like Adam Wenger said you'll need to inner join them. Inner joins will return rows when there is at least 1 match in all joined tables.
If you need to ensure that the result is also in Table A, you're going to need to join that one too:
SELECT c.Id, b.Value
FROM B
INNER JOIN A ON B.attributeId = A.ID
INNER JOIN C ON B.attributeId = C.attributeId
WHERE B.fooId = 25
AND C.attributeId = -1
ORDER BY C.DisplayIndex
Related
I have this structure:
Table A -- |id_A | field_1a | id_B | value_A|
Table B -- |id_B | field_1b | field_2b | value_B|
Table C -- |field_1c | id_D | id_A|
Table D -- |id_D | description|
I want to get a query which returns:
-- Value A and if this value is null, returns its value in B.
-- Description of Table D through Table C. If row is not in C returns null.
I achieved the first part but I am stuck in the second part. As far as I tried this is my query:
select a.id_A
if (VALOR_b is null, VALOR_a, VALOR_b) as valor,
d.description
from A a inner join B b
on a.id_B = b.id_B
inner join C c
on c.id_A = A.id_A
inner join D d
on d.id_D = c.D
As I said I am getting the first part and just the values what I can cross through C, but I need when I can cross them a null value in the previously part of the query.
Hoping I explain clear enough. Please, ask me any doubt.
Thanks in advance.
Use a left join to both C and D.
Also your life will be easier if you use the SQL standard coalesce() instead of if ():
select
a.id_A,
coalesce(VALOR_a, VALOR_b) as valor,
d.description
from A a
join B b on a.id_B = b.id_B
left join C c on c.id_A = A.id_A
left join D d on d.id_D = c.D
Left join still returns a row from the parent table if there is no matching row, in which case it returns all nulls from the joined table"
coalesce() takes any number of arguments and returns the first non-null value.
This is the query:
SELECT a.id, a.userName,if(o.userId=1,'C',if(i.userId=1,'I','N')) AS relation
FROM tbl_users AS a
LEFT JOIN tbl_contacts AS o ON a.id = o.contactId
LEFT JOIN tbl_invites AS i ON a.id = i.invitedId
ORDER BY relation
This returns the output as follows:
+----+--------------+-------------+
| ID | USERNAME | RELATION |
+----+--------------+-------------+
| 1 | ray | C |
+----+--------------+-------------+
| 2 | john | I |
+----+--------------+-------------+
| 1 | ray | N |
+----+--------------+-------------+
I need to remove the third row from the select query by checking if possible that id is duplicate. The priority is as follows:
C -> I -> N. So since there is already a "ray" with a C, I dont want it again with an I or N.
I tried adding distinct(a.id) but it doesn't work. How do I do this?
Why doesn't DISTINCT work for this?
From the specs you gave, all you have to do is group by ID and username, then pick the lowest value of relation you can find (since C < I < N)
SELECT a.id, a.userName, MIN(if(o.userId=1,'C',if(i.userId=1,'I','N'))) AS relation
FROM tbl_users AS a
LEFT JOIN tbl_contacts AS o ON a.id = o.contactId
LEFT JOIN tbl_invites AS i ON a.id = i.invitedId
GROUP BY a.id, a.username
There are multiple ways to get the group-wise maximum/minimum as you can see in this manual page.
The best one suited for you is the first one, if the order of the rows can not be defined by alphabetic order.
In this case, given if the desired order were z-a-m (see Rams' comment) you'd need the FIELD() function.
So your answer is
SELECT
a.id,
a.userName,
if(o.userId=1,'C',if(i.userId=1,'I','N')) AS relation
FROM tbl_users a
LEFT JOIN tbl_contacts AS o ON a.id = o.contactId
LEFT JOIN tbl_invites AS i ON a.id = i.invitedId
WHERE
if(o.userId=1,'C',if(i.userId=1,'I','N')) = (
SELECT
if(o.userId=1,'C',if(i.userId=1,'I','N')) AS relation
FROM tbl_users aa
LEFT JOIN tbl_contacts AS o ON aa.id = o.contactId
LEFT JOIN tbl_invites AS i ON aa.id = i.invitedId
WHERE aa.id = a.id AND aa.userName = a.userName
ORDER BY FIELD(relation, 'N', 'I', 'C') DESC
LIMIT 1
)
Note, you can also do it like ORDER BY FIELD(relation, 'C', 'I', 'N') to have it more readable / intuitive. I turned it the other way round, because if you'd have the possibility of having a 'X' in the relation, the FIELD() function would have returned 0 because X is not specified as a parameter. Therefore it would be sorted before 'C'. By sorting descending and turning the order of the parameters around this can not happen.
I don't know if this question is apropriate on this forum.
I have a huge query :
SELECT threshold.id, brand.id, COUNT(brand.id), threshold
FROM current_stock, article, product, brand, delivery, threshold
WHERE current_stock.article_id = article.id
AND article.product_product_code = product.product_code
AND product.brand_id = brand.id
AND article.delivery_id = delivery.id
AND delivery.store_id = 'E260'
AND threshold.brand_id = brand.id
GROUP BY brand.id
HAVING COUNT(brand.id) <= threshold
UNION
SELECT threshold.id, brand.id, 0, threshold
FROM current_stock, article, product, brand, delivery, threshold
WHERE threshold.store_id = 'E260'
AND threshold.brand_id NOT IN (
SELECT brand_id FROM current_stock, article, product, delivery
WHERE current_stock.article_id = article.id
AND article.product_product_code = product.product_code
AND article.delivery_id = delivery.id
AND delivery.store_id = 'E260')
And I think it's possible to do better but after a entire day of try I haven't found a better query giving the same result.
For clarify, I have a stock (with current_stock, article, product and delivery). I also have thresholds. what I want is to check for each thresholds if there is the given minimum amount of stock for the given brand.
My problem is that if there is 0 article of a brand, the first part of the query will not take care about the threshold on this brand. It's why I have added an uggly Union.
Someone have an idea for a better way to do this ?
EDIT
This what I have done after the reading of comments and answers :
SELECT t.id, b.id, t.threshold, count(b.id) stock
FROM threshold t
inner join brand b on b.id = t.brand_id
left join product p on p.brand_id = b.id
inner join article a on a.product_product_code = p.product_code
inner join delivery d on d.id = a.delivery_id
inner join current_stock cs on cs.article_id = a.id
WHERE
t.store_id = 'E260' AND
d.store_id = 'E260'
GROUP BY b.id
HAVING stock <= t.threshold
My problem is that it don't gives all threholds... only ones that have at least one 'current_stock'. I have perhaps don't understand how joins are working.
Here an example of threshold table :
| id | brand_id | threshold |
-----------------------------
| 1 | 86 | 1 |
| 2 | 28 | 1 |
| 3 | 12 | 1 |
What I want as result this :
# with 2 entries in 'current_stock' for the brand id 28, 1 for 12 and 0 for 86
| t.id | b.id | threshold | stock |
-----------------------------------
| 1 | 86 | 1 | 0 |
| 3 | 12 | 1 | 1 |
Guessing a few parts here since you've used implicit joins in your sample. An explicit version would look something like this (provided I guessed correctly for how you are joining the threshold table).
SELECT
t.id,
b.id,
COUNT(b.id),
t.threshold
FROM
current_stock c
inner join article a on a.id = c.article_id
inner join delivery d on d.id = a.delivery_id
inner join product p on p.product_code = a.product_product_code
inner join brand b on b.id = p.brand_id
inner join threshold t on t.brand_id = b.id
WHERE
d.store_id = 'E260'
GROUP BY b.id
HAVING COUNT(b.id) <= t.threshold
Now to get your results to include rows where there aren't any 'articles' you can start switching out the inner joins for left joins. However, you can't simply use left outer join article... in the example above, because the store_id in the WHERE clause will just turn it back into a pseudo inner join.
Instead, is there a different field you can join the delivery table on from current_stock?
EDIT - 07/29/15
I think you're close, you may just have one too many filters and you're counting from 'b' when the wanted outcome suggests you should be counting from 'cs' instead. Try this:
SELECT t.id, b.id, t.threshold, count(cs.id) stock
FROM
threshold t
inner join brand b on b.id = t.brand_id
inner join product p on p.brand_id = b.id
inner join article a on a.product_product_code = p.product_code
left outer join delivery d on d.store_id = t.store_id
left outer join current_stock cs on cs.article_id = a.id
WHERE
t.store_id = 'E260'
GROUP BY b.id
HAVING stock <= t.threshold
Say I have these data from two table:
Student Table columns:
id | name
Course Table columns:
id | code | name
and I want to use the Student.id AS Student and Course.id AS Course
to get the following:
Student | Course
-----------------
1 | C
1 | B
1 | A
2 | F
2 | B
2 | A
3 | C
3 | B
3 | F
How would I query it so it will return only the Students with a Course C and their other Courses like below:
Student | Course
-----------------
1 | C
1 | B
1 | A
3 | C
3 | B
3 | F
?
I have tried :
SELECT Student.id, Course.code FROM Course
INNER JOIN Student ON Course.student = Student.id
WHERE Course.code = 'C'
but I got only
Student | Course
-----------------
1 | C
3 | C
SELECT s.id, c.code
FROM Course c
INNER JOIN Student s
ON c.student = s.id
WHERE EXISTS
(
SELECT 1
FROM Course c1
WHERE c.student = c1.student
AND c1.Course = 'C'
)
The most efficient approach to this problem is usually an inline view and a JOIN operation, although there are several ways to get an equivalent result.
SELECT Student.id
, Course.code
FROM ( SELECT c.Student
FROM Course c
WHERE c.code = 'C'
GROUP BY c.Student
) o
JOIN Course
ON Course.Student = o.Student
JOIN Student
ON Student.id = Course.Student
Here, we're using an inline view (aliased as o) to get a list of Student taking course code = 'C'.
(NOTE: the query in my answer is based on your original query. If there's a foreign key definition between Course and Student, and we only need to return the Student.id, we could improve performance by omitting the join to Student, and return Course.Student AS id in place of Student.id in the SELECT list.)
Here the first JOIN selects only those students which have course C, and second JOIN gives you all the courses for each of those students.
SELECT st.id, c2.code FROM
Student st
JOIN Course c ON c.student = st.id AND c.code = "C"
JOIN Course c2 ON c2.student = st.id
You actually don't even need two tables here, because both student and course is available in the Course table, just JOIN it on itself:
SELECT c2.student, c2.code FROM
Course c JOIN Course c2 ON c.student = c2.student
WHERE c.course = "C"
Here the WHERE clause leaves student id's which have course C and then you JOIN those to find all their courses.
I have this database structure:
TBL_A | TBL_B | TBL_C | TBL_D | TBL_E
-------+---------+---------+---------+----------
id | id_tbla | id_tbla | id_tbla | id
name | id_user | id_user | id_user | name_tbla
... | is_bool | | weight | id_user
Here is what I'm trying to achieve :
SELECT
a.id,
a.name,
b.is_bool,
count(c.id_user) AS nb_views,
sum(d.weight) AS total_weight,
count(distinct e.id_user) AS distinct_users,
FROM TBL_A AS a
LEFT JOIN (TBL_B AS b) on (b.id_tbla = a.id)
LEFT JOIN (TBL_C AS c) on (c.id_tbla = a.id)
LEFT JOIN (TBL_D AS d) on (d.id_tbla = a.id)
LEFT JOIN (TBL_E AS e) on (e.name_tbla = a.name)
where a.id = 1 and e.id_user = 1
The query is performed but the results (nb_views, total_weight, distinct_users) are wrong. Any idea why?
You're trying to compute too many aggregates in one query.
Enita non sunt multiplicanda praeter necessitatem
(Latin, "entities are not to be multiplied beyond necessity")
Your tables B, C, D, and E are produced Cartesian Products against each other. Suppose the
given row in A matches:
3 rows in B
6 rows in C
4 rows in D
1 row in E
The total number of rows in the result is 3 * 6 * 4 * 1 = 72 rows. So your count(c.id_user) is 12 times what it should be, your sum(d.weight) is 18 times what it should be, etc.
The simplest remedy is to compute each of these aggregates in a separate query:
SELECT a.id, a.name, COALESCE(b.is_bool, FALSE) AS is_bool
FROM TBL_A AS a LEFT JOIN TBL_B AS b ON (b.id_tbla = a.id)
WHERE a.id = 1;
SELECT a.id, COUNT(c.id_user) AS nb_views
FROM TBL_A AS a LEFT JOIN TBL_C AS c ON (c.id_tbla = a.id)
WHERE a.id = 1;
SELECT a.id, SUM(d.weight) AS total_weight,
FROM TBL_A AS a LEFT JOIN TBL_D AS d ON (d.id_tbla = a.id)
WHERE a.id = 1;
SELECT a.id, COUNT(DISTINCT e.id_user) AS distinct_users,
FROM TBL_A AS a LEFT JOIN TBL_E AS e
ON (e.name_tbla = a.name AND e.id_user = 1)
WHERE a.id = 1;