I have a table category which has fields and values as shown below in MYSQL database.
id name parent sort_order
1 Men null 0
2 Women null 1
3 shirt 1 0
4 salwar 2 1
Here parent is a foreign key points to the same table. In my category list page i want to print the parent hierarchy(if any) along with the category name. can i do this in a single query.
I have tried with group_concat in mysql but not able to generate the required result.
Expected Result:
1 men
2. women
3. men>shirt
4. women> salwar
You can use a self-join:
SELECT *
FROM
(
SELECT name, 1 AS rank, sort_order
FROM category
WHERE parent IS NULL
UNION ALL
SELECT CONCAT(c1.name,
CASE WHEN c2.parent IS NOT NULL THEN CONCAT('>', c2.name) ELSE '' END), 0 AS rank, c1.sort_order
FROM category c1 LEFT JOIN category c2
ON c1.id = c2.parent
WHERE c1.parent IS NULL
) t
ORDER BY t.rank DESC, t.sort_order
SQLFiddle
Related
This question already asked but that not solve my issue.
I have a table given below table name categories. I want to fetch all the category with separated >. Parent category data and Sub category data in same table.
categoryId categoryName categorytype parentCategoryId status
1 parent category 0 0 1
2 Sub category 1 1 1
So I want to fetch the data like this
Output:
categoryId categoryName categorytype parentCategoryId status
1 parent category 0 0 1
2 parent category > Sub category 1 1 1
Only Sub category I want to add parent category as mentioned above.
I tried this query
SELECT * FROM categories c1 LEFT JOIN categories c2 ON c2.categoryId = c1.parentCategoryId;
Current output:
Please help me to solve this, thanks in advance.
You query joins are OK, selecting right columns will do.
SELECT c1.categoryId, CONCAT((CASE WHEN c2.categoryId IS NOT NULL THEN CONCAT(c2.categoryName, ' > ') ELSE '' END), c1.categoryName) categoryName, c1.categoryType, c1.parentCategoryId, c1.status
FROM categories c1
LEFT JOIN categories c2 ON c2.categoryId = c1.parentCategoryId
It assumes your category structure is parent-sub two levels only.
I want to join columns from multiple tables to one column, in my case column 'battery_value' and 'technical_value' into column 'value'. I want to fetch data for only given category_ids, but because of UNION, I get data from other tables as well.
I have 4 tables:
Table: car
car_id model_name
1 e6
Table: battery
battery_category_id car_id battery_value
1 1 125 kW
Table: technical_data
technical_category_id car_id technical_value
1 1 5
3 1 2008
Table: categories
category_id category_name category_type
1 engine power battery
1 seats technical
3 release year technical
From searching, people are suggesting that I use union to join these columns. My query now looks like this:
SELECT CARS.car_id
category_id,
CATEGORIES.category_name,
value,
FROM CARS
left join (SELECT BATTERY.battery_category_id AS category_id,
BATTERY.car_id AS car_id,
BATTERY.value AS value
FROM BATTERY
WHERE `BATTERY`.`battery_category_id` IN (1)
UNION
SELECT TECHNICAL_DATA.technical_category_id AS category_id,
TECHNICAL_DATA.car_id AS car_id,
TECHNICAL_DATA.value AS value
FROM TECHNICAL_DATA
WHERE `TECHNICAL_DATA`.`technical_category_id` IN (3))
tt
ON CARS.car_id = tt.car_id
left join CATEGORIES
ON category_id = CATEGORIES.id
So the result I want is this, because I only want to get the data where category_id 1 is in battery table:
car_id category_id category_name technical_value
1 1 engine power 125 kW
1 3 release year 2008
but with the query above I get this, category_id 1 from technical table is included which is not something I want:
car_id category_id category_name value
1 1 engine power 125 kW
1 1 seats 125 kW
1 3 release year 2008
How can get exclude the 'seats' row?
For the results you want, I don't see why the cars table is needed. Then, you seem to need an additional key for the join to categories based on which table it is referring to.
So, I suggest:
SELECT tt.*, c.category_name
FROM ((SELECT b.battery_category_id AS category_id,
b.car_id AS car_id, b.value AS value,
'battery' as which
FROM BATTERY b
WHERE b.battery_category_id IN (1)
) UNION ALL
(SELECT td.technical_category_id AS category_id,
td.car_id AS car_id, td.value AS value,
'technical' as which
FROM TECHNICAL_DATA td
WHERE td.technical_category_id IN (3)
)
) tt LEFT JOIN
CATEGORIES c
ON c.id = tt.category_id AND
c.category_type = tt.which;
That said, you seem to have a problem with your data model, if the join to categories requires "hidden" data such as the type. However, that is outside the scope of the question.
I am trying to understand how this subquery works. The questions are as follows
Mary is a teacher in a middle school and she has a table seat storing students' names and their corresponding seat ids.The column id is continuous increment.
Mary wants to change seats for the adjacent students.
SELECT
(CASE
WHEN MOD(id, 2) != 0 AND counts != id THEN id + 1
WHEN MOD(id, 2) != 0 AND counts = id THEN id
ELSE id - 1
END) AS id,
student
FROM
seat,
(SELECT
COUNT(*) AS counts
FROM
seat) AS seat_counts
ORDER BY id ASC;
I am trying to understand the how the above query works. So in the CASE it checks if the id is odd or even and checks against the count to see if it is the last element. But how does the ORDER BY ASC work? Because for the first time it selects student Dorris and id 2. but then how is id 2 assigned to Abbot. Thanks.
SQL Table
id | student
1 | Abbot
2 | Doris
3 | Emerson
4 | Green
5 | Jeames
The Result will look like
id | student
1 | Dorris
2 | Abbot
3 | Green
4 | Emerson
5 | Jeames
OK what this is doing is the following -- if an id number is odd and it is not the max number then add one to it, otherwise subtract one from it.
It should be clear that would swap all but the last pair.
I think it is badly written I would write it like this:
WITH student_count(max) as
(
SELECT COUNT(*) FROM seat
)
SELECT
CASE
WHEN student_count.max != id AND MOD(id, 2) != 0 THEN id + 1
WHEN student_count.max != id AND MOD(id, 2) = 0 THEN id - 1
ELSE id
END AS id,
student
FROM seat
CROSS JOIN student_count
ORDER BY id ASC;
I would recommend you to check the results by removing ORDER BY statement. When you remove ORDER BY statement, result will be:
2 Abbot
1 Doris
4 Emerson
3 Green
5 Jeames
Which is completely right for your case. Basically, your query just alters id's values based on the CASE statement. When you add ORDER BY id ASC statement it just orders the result above.
select name,
case when mod(seat_id,2) = 1 and seat_id <> (select max(seat_id) from students) then seat_id + 1
when mod(seat_id,2)= 0 then seat_id - 1
when mod(seat_id,2) = 1 and seat_id = (select max(seat_id) from students) then seat_id
end swap
from students
SELECT
(CASE
WHEN MOD(id, 2) != 0 AND counts != id THEN id + 1
WHEN MOD(id, 2) != 0 AND counts = id THEN id
ELSE id - 1
END) AS id,
student
FROM
seat,
(SELECT
COUNT(*) AS counts
FROM
seat) AS seat_counts
ORDER BY id ASC;
I have a table like this:
userid | trackid | path
123 70000 ad
123 NULL abc.com
123 NULL Apply
345 70001 Apply
345 70001 Apply
345 NULL Direct
345 NULL abc.com
345 NULL cdf.com
And I want a query like this. When path='abc.com', num_website +1; when path='Apply', num_apply +1
userid | num_website | num_Apply | num_website/num_Apply
123 1 1 1
345 1 2 0.5
My syntax looks like this:
select * from
(select userid,count(path) as is_CWS
from TABLE
where path='abc.com'
group by userid
having count(path)>1) a1
JOIN
(select userid,count(userid) as Apply_num from
where trackid is not NULL
group by userid) a2
on a1.userid=a2.userid
My question is
1. how to have the field num_website/num_apply in term of my syntax above?
2. is there any other easier way to get the result I want?
Any spots shared will appreciate.
The simplest way to do it would be to change the select line:
SELECT a1.userid, a1.is_CWS, a2.Apply_num, a1.is_CWS/a2.Apply_num FROM
(select userid,count(path) as is_CWS
from TABLE
where path='abc.com'
group by userid
having count(path)>1) a1
JOIN
(select userid,count(userid) as Apply_num
from TABLE
where trackid is not NULL
group by userid) a2
on a1.userid=a2.userid
and then continue with the rest of your query as you have it. The star means "select everything." If you wanted to select only a few things, you would just list those things in place of the star, and if you wanted to select some other values based on those things, you would put those in the stars as well. In this case a1.is_CWS/a2.Apply_num is an expression, and MySql knows how to evaluate it based on the values of a1.is_CWS and a2.Apply_num.
In the same vein, you can do a lot of what those subqueries are doing in a single expression instead of a subquery. objectNotFound has the right idea. Instead of doing a subquery to retrieve the number of rows with a certain attribute, you can select SUM(path="abc.com") as Apply_num and you don't have to join anymore. Making that change gives us:
SELECT a1.userid,
SUM(path="abc.com") as is_CWS,
a2.Apply_num,
is_CWS/a2.Apply_num FROM
TABLE
JOIN
(select userid,count(userid) as Apply_num
FROM TABLE
where trackid is not NULL
group by userid) a2
on a1.userid=a2.userid
GROUP BY userid
Notice I moved the GROUP BY to the end of the query. Also notice instead of referencing a1.is_CWS I now reference just is_CWS (it's no longer inside the a1 subtable so we can just reference it)
You can do the same thing to the other subquery then they can share the GROUP BY clause and you won't need the join anymore.
to get you started ... you can build on top of this :
select
userid,
SUM(CASE WHEN path='abc.com'then 1 else 0 end ) as num_website,
SUM(CASE WHEN path='Apply' and trackid is not NULL then 1 else 0 end ) as Apply_Num
from TABLE
WHERE path='abc.com' or path='Apply' -- may not need this ... play with it
group by userid
I need help with SQL request.
I have 3 tables:
Table User
id name
1 Jon
2 Jack
3 Bill
Table Type
id name
1 View
2 Edit
3 Delete
Table Right
id user type
1 1 1
2 1 2
3 1 3
4 2 1
5 3 1
So table Right contains linked pairs of user-type. I need a request which gets user name, and a boolean (BIT) value for each enrty in table Type, which exists in Right table for this user. Something like this for my example tables:
Username View Edit Delete
Jon 1 1 1
Jack 1 0 0
Bill 1 0 0
Thank you very much in advance!
untested:
select name,
coalesce(select 1 from `right` where `type` = 1 and right.user = user.id, 0) as `View`,
coalesce(select 1 from `right` where `type` = 2 and right.user = user.id, 0) as `Edit`,
coalesce(select 1 from `right` where `type` = 3 and right.user = user.id, 0) as `Delete`
from User
Alternatively:
select name, coalesce(RVIEW.R, 0) as `View`, coalesce(REDIT.R, 0) as `Edit`, coalesce(RDEL.R, 0) as `Delete`
from User
left join (select 1 R from `right` where `type` = 1) RVIEW on (right.user = user.id)
left join (select 1 R from `right` where `type` = 2) REDIT on (right.user = user.id)
left join (select 1 R from `right` where `type` = 3) RDEL on (right.user = user.id)
In your example, you are using reserved words as table names.
If you want to learn more about naming conventions for table names, have a look at the links in an earlier question on Stack Overflow here
Example below shows yet another way of getting the data you want (with other names for the tables):
select person.name as Username
, max( if( person_right.type_id = 1, 1, 0 ) ) as `View`
, max( if( person_right.type_id = 2, 1, 0 ) ) as `Edit`
, max( if( person_right.type_id = 3, 1, 0 ) ) as `Delete`
from person
left outer join person_right
on person_right.user_id = person.id
group by person.name
order by person.id
Another thing that might be worth looking at is the datamodel,
because Rights are normally quite "fixed".
If anyone accidentally changes one of the names in the Type table, you might have a serious security issue.
What you can do is change the person_right table to look like this
windowid user_id view_access edit_access delete_access
1 1 1 1 1
1 2 1 0 0
1 3 1 0 0
where the primary key would be window_id+user_id allowing you to setup different rights per user in a particular window/part of your application.
Hope this helps.