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).
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
$query='SELECT * FROM #__virtuemart_products as a
LEFT JOIN #__virtuemart_products_en_gb as b ON a.virtuemart_product_id = b.virtuemart_product_id
INNER JOIN #__virtuemart_product_categories as c ON a.virtuemart_product_id=c.virtuemart_product_id
INNER JOIN #__virtuemart_categories_en_gb as d ON c.virtuemart_category_id = d.virtuemart_category_id
WHERE b.slug LIKE "'.$current.'%" AND a.product_parent_id = 0
AND d.category_name="'.$query_title.'"' ;
$db->setQuery($query);
$options=$db->loadObjectList();
This is the query i use to parse some products from my db. The problem is:
Table: virtuemart_products_en_gb has a collumn named slug
Table: virtuemart_categories_en_gb has also a collumn named slug
When i used $row->slug it parsed the virtuemart_categories_en_gb slug.
So after i var_dumped the ObjectList i see that there is only 1 collumn named slug. After i used the same query in phpmyadmin, it returns me 2 collumns named slug.
I think i could fix that selecting every single record individual and setting first slug as slug1 and second as slug2.
For example: SELECT id,username,password,b.slug as slug1,c.slug as slug2 etc
Is there any better way ? Cause i need to parse really many fields and that would make the query really huge.And why the php query returns only 1 field named slug while phpmyadmin returns both of em ?
Thanks in advance.
You can specify * after selecting the columns with the same name. For example,
SELECT *, b.slug as slug1,c.slug as slug2
FROM #__virtuemart_products as a
LEFT JOIN #__virtuemart_products_en_gb as b ON a.virtuemart_product_id = b.virtuemart_product_id
INNER JOIN #__virtuemart_product_categories as c ON a.virtuemart_product_id=c.virtuemart_product_id
INNER JOIN #__virtuemart_categories_en_gb as d ON c.virtuemart_category_id = d.virtuemart_category_id
WHERE b.slug LIKE "'.$current.'%" AND a.product_parent_id = 0
AND d.category_name="'.$query_title.'"
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 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.
I'm very new with SQL and need assistance on how I can accomplish this task using the correct query.
I have 2 tables that I need to use. Table "TB1" has:
id Name
1 bob
2 blow
3 joe
table "TB2" has:
compid property
1 bob
2 blow
I am trying to get which compid is missing in "TB2" and insert it from "TB1"
the query I am doing is:
SELECT id, name from TB1, TB2 where id <> compid
what I get is 2 ouputs of Id 1, and 2, and 3 outputs from id 3. by using php:
for($i=0;$i <= mysql_num_rows($comp)-1; $i++)
{
echo mysql_result($comp, $i, 0)."<br>";
}
and I expected the ouput 3 but instead got this:
1
1
2
2
3
3
3
I understand its comparing all the rows within the table but is there a way to achieve what I am looking for?
Thanks for your time.
You are performing an implicit Cartesian JOIN which results in every row against every other row. You need to specify what attribute JOINs the two tables.
Using implicit syntax (not recommended):
SELECT id, name
FROM TB1, TB2
WHERE id <> compid
AND TB1.Name = TB2.property <-- Column join
Using explicit syntax:
SELECT id, name
FROM TB1
JOIN TB2
ON TB2.property = TB1.Name <-- Column join
WHERE id <> compid
To accomplish your goal you would need something along the lines of:
SELECT TB1.id, TB1.name
FROM TB1
LEFT JOIN TB2
ON TB2.property = TB1.Name
WHERE TB2.compid IS NULL
See it in action
It's best practice to always alias the columns you select to prevent ambiguity.
To select it you can do:
SELECT *
FROM TB1
WHERE id NOT IN (
SELECT compid
FROM TB2
);