I have a table like this:
**id name parent_id**
1 X 2
2 Y 2
3 Z 1
4 A 5
5 B 6
6 C 1
I want output look like this:
**name *parent name***
X Y
Y Y
Z X
A B
B C
C X
Is it possible to do it with one query by using JOIN?
You need to perform a self-join:
SELECT child.name AS `name`, parent.name AS `parent name`
FROM my_table AS child JOIN my_table AS parent ON parent.id = child.parent_id
See it on sqlfiddle.
select son.name as name, father.name as parent_name from table_name as son left join table_name as father ON son.parent_id = father.id
Let's say you have 2 tables:
product
product_parent
Then, you run a query like this:
SELECT product.name, product_parent.name
FROM product
INNER JOIN product_parent
ON product.product_parent_id=product_parent.id
You can use JOIN to do this
Example:
SELECT
table.name
, parent.name as parent_name
FROM
table
LEFT JOIN
parent ON parent.parent_id = table.parent_id
WHERE
table.visible = 1
After that you will handle the response from your query in php cycle through returned array of items(array's or object's - depends on what MySQL abstraction you use), save the needed in your own array, or just encoding this array to JSON.
Note: I don't know for what you need this, but it's good idea to include table.id in the result, if you want latter to be able to identify one record.
Related
I have a similar question to How to use GROUP BY to concatenate strings in MySQL? , however for this example for mytable table
id string aggr
1 A NULL
1 B NULL
2 F NULL
The difference is I need to update the table to get this results:
id string aggr
1 A A|B|
1 B A|B|
5 C C|E|C|
5 E C|E|C|
5 C C|E|C|
2 F F|
As result the same id we have the same newcolumn values.
It is absolutely fine to add a delimiter |at the very end of the string. That way I can even faster count how many "items" are in the newcolumn without adding +1 because of the absense at the very end (just in between). Also I won't care about validation (if I have a pipe right before) when appending another part or two into aggr column.
Thank you.
You can try this query :
UPDATE my_table t
SET aggr = (
SELECT * FROM (
SELECT CONCAT(GROUP_CONCAT(t2.string SEPARATOR '|'), '|')
FROM my_table t2
WHERE t2.id = t.id
) AS X
)
You could a group_concat joined on original table
select a.id, a.string , b.aggr
from my_table a
inner join (
select id, group_concat(string SEPARATOR '|') as aggr
from my_table
group by id
) b on a.id = b.id
I have a table named property ,structured like this.
property_id | ListingKey | name
1 abkjhj-123 abc
2 abkjhj-123 abc1
3 abkjhj-124 abc4
I want duplicate records based on ListingKey. I write this query but not sure is this correct or not?
SELECT a.property_id
FROM property a
INNER JOIN property b ON a.property_id = b.property_id
WHERE a.ListingKey <> b.ListingKey
Thanks in advance.
You can avoid the self join with a Having clause:
SELECT a.ListingKey
FROM property a
GROUP BY a.ListingKey
HAVING COUNT(a.property_id) > 1;
SqlFiddle
Update : If you want a list of all the ids in the Duplicate as well:
SELECT a.ListingKey, GROUP_CONCAT(a.property_id)
FROM property a
GROUP BY a.ListingKey
HAVING COUNT(a.property_id) > 1;
Your query is not correct. Here is another method:
select p.*
from property p
where exists (select 1
from property p2
where p2.listingkey = p.listingkey and p2.property_id <> p.property_id
);
If you care about performance, add an index on property(listingkey, property_id).
I just wrote this query for my tables: NEWS and NEWS-CATEGORIES in order to count the items of each category:
SELECT DISTINCT CAT.cid, CAT.c_title, N.n_category, count(*) AS cat_count
FROM news N
inner join news - categories CAT
on CAT.cid = N.n_category
GROUP BY N.n_category
but the problem is that it just shows me the categories which contains news! but I wana get all of the categories even the ones with empty news...
my NEWS table is:
nid | n_category | etc
my NEWS-CATEGORY table is:
cid | c_title | etc
Thanks for your help
Regards
Try this:
SELECT
CAT.cid,
CAT.c_title,
count(N.n_category) AS cat_count
FROM `news-categories` CAT
LEFT JOIN `news` N
ON CAT.cid = N.n_category
GROUP BY CAT.cid,
CAT.c_title
Use LEFT JOIN:
SELECT CAT.cid, CAT.c_title, IFNULL(COUNT(N.n_category), 0) AS cat_count
FROM `news-categories` AS CAT
LEFT JOIN news AS N ON CAT.cid = N.n_category
GROUP BY CAT.cid
Things to note: 1) You have to use a column from news in the COUNT() expression, not COUNT(*), so that the null match is not counted. 2) There's no need to select N.n_category, since that's always equal to CAT.cid and you're already selecting that. 3) The GROUP BY column has to be from the news-categories table -- you can't group by a column in the table that may not have any matching rows, since that value will always be NULL.
I'm just going to point out that you can do this with a subquery as well:
SELECT CAT.cid, CAT.c_title,
(SELECT COUNT(*) FROM news N WHERE CAT.cid = N.n_category)
FROM `news - categories` CAT;
Under some circumstances, this can even have better performance.
I have two table 'topic' and 'subcategory'
I am using this query--
Select * from `subcategory` as s
Inner join `topic` as f
WHERE s.`Subcategory_id` = f.`Subcategory_id
My result shows like
Category_id Subcategory_id Post_id time
2 2.3 4 2012-12-01
1 1.5 5 2013-01-20
1 1.3 6 2013-03-18
There's also other columns... but all I want is to select the latest Post_id and Subcategory_id of one Category_id ... that means here Category 1 has two Subcategory it will select only the latest(here 1.3) and same result all the time for all Category when database will grown larger. What will be the next query or how could I change the existing query to gain my desired result?
SELECT Post_Id, Subcategory_Id from subcategory as s, topic as t where
s.Subcategory_id = t.Subcategory_id and time = (
SELECT Max(time) from subcategory as s1, topic as t1 where
s1.Subcategory_id = t1.Subcategory_id and s1.Category_id = s.Category_id
);
Something like that, I think, will work.
SELECT TOP 1 ... ORDER BY whatever column determines "the latest"
e.g.
SELECT TOP 1 ... ORDER BY TIME DESCENDING
Or in case of mysql:
SELECT ... ORDER BY TIME DESCENDING LIMIT 1
Join your topic table with following query:
SELECT s.* FROM subcategory s
Inner JOIN (SELECT s1.Category_id,
MAX(s1.time1) AS max_time
FROM subcategory s1
GROUP BY s1.Category_id) y
ON y.Category_id = s.Category_id AND y.max_time = s.time1
I have an instrument list and teachers instrument list.
I would like to get a full instrument list with id and name.
Then check the teachers_instrument table for their instruments and if a specific teacher has the instrument add NULL or 1 value in a new column.
I can then take this to loop over some instrument checkboxes in Codeigniter, it just seems to make more sense to pull the data as I need it from the DB but am struggling to write the query.
teaching_instrument_list
- id
- instrument_name
teachers_instruments
- id
- teacher_id
- teacher_instrument_id
SELECT
a.instrument,
a.id
FROM
teaching_instrument_list a
LEFT JOIN
(
SELECT teachers_instruments.teacher_instrument_id
FROM teachers_instruments
WHERE teacher_id = 170
) b ON a.id = b.teacher_instrument_id
my query would look like this:
instrument name id value
--------------- -- -----
woodwinds 1 if the teacher has this instrument, set 1
brass 2 0
strings 3 1
One possible approach:
SELECT i.instrument_name, COUNT(ti.teacher_id) AS used_by
FROM teaching_instrument_list AS i
LEFT JOIN teachers_instruments AS ti
ON ti.teacher_instrument_id = i.id
GROUP BY ti.teacher_instrument_id
ORDER BY i.id;
Here's SQL Fiddle (tables' naming is a bit different).
Explanation: with LEFT JOIN on instrument_id we'll get as many teacher_id values for each instrument as teachers using it are - or just a single NULL value, if none uses it. The next step is to use GROUP BY and COUNT() to, well, group the result set by instruments and count their users (excluding NULL-valued rows).
If what you want is to show all the instruments and some flag showing whether or now a teacher uses it, you need another LEFT JOIN:
SELECT i.instrument_name, NOT ISNULL(teacher_id) AS in_use
FROM teaching_instrument_list AS i
LEFT JOIN teachers_instruments AS ti
ON ti.teacher_instrument_id = i.id
AND ti.teacher_id = :teacher_id;
Demo.
Well this can be achieved like this
SELECT
id,
instrument_name,
if(ti.teacher_instrument_id IS NULL,0,1) as `Value`
from teaching_instrument_list as til
LEFT JOIN teachers_instruments as ti
on ti.teacher_instrument_id = til.id
Add a column and check for teacher_instrument_id. If found set Value to 1 else 0.