I have a table that stores values for attributes associated to products.
row_id product_id attribute_id value
1 1 1 a
2 1 2 b
3 2 1 d
4 2 2 e
How do i write a select to get the value for attribute_id=2 only for products that have value="a" for attribute_id=1?
Thanks,
Have a nice day
Maybe this is what you want?
select *
from your_table
where attribute_id = 2
and product_id in (
select product_id
from your_table
where attribute_id = 1 and value = 'a'
)
With your sample data the row with row_id = 2 would be returned.
Related
I would like to update row using next couple of rows.
I have database like
id Product_number qty parent_id type
1 AAAA null PRODUCT
2 bbb 5 1 ITEM
3 ccc 8 1 ITEM
I have this type of data into table, so I want to update qty column of that row where type is PRODUCT using min value of those rows where parent_id is id of row which has column type value PRODUCT etc
so result should be
id Product_number qty parent_id type
1 AAAA 5 null PRODUCT
2 bbb 5 1 ITEM
3 ccc 8 1 ITEM
Is this what you want?
update t join
(select parent_id, min(qty) as min_qty
from t
group by parent_id
) tt
on t.id = tt.parent_id
set t.qty = tt.min_qty
where t.qty is null and t.type = 'ITEM';
I need to count matches in a database.
Input:
id_to id_from
1 2
2 1
1 3
3 1
1 4
5 1
the 5th and 6th row has only one direction so doesn't count
Sample Output:
id_match
1
2
3
So, for 1 (implicit), 2 and 3 there is a reverse match but for 4 and 5 there aren't.
---- EDITED ----
Supposing the table name is "example" and I want to get all matches of id=1 then the SQL query will be:
SELECT count(*) FROM
(SELECT id_to FROM example WHERE id_from = 1) as t1,
(SELECT id_from FROM example WHERE id_to = 1) as t2
WHERE t1.id_to = t2.id_from
but maybe there is a better way to do it
You could try
SELECT DISTINCT id_from AS matched_id
FROM your_table AS data1
WHERE EXISTS (SELECT 1
FROM your_table AS data2
WHERE data1.id_from = data2.id_to
AND data1.id_to = data2.id_from)
I've created a demo here
id name count
------------
1 abc
2 xyz
3 xyz
4 xyz
The following query "select count(name) from temp group by name;" gives me:
count(name)
--------
1
3
I want this result to be updated to the column 'count'. To be precise I want my table to look like :
id name count
------------
1 abc 1
2 xyz 3
3 xyz 3
4 xyz 3
You can get those values with a COUNT / GROUP BY. You can do an UPDATE statement which joins your table with the sub query:-
UPDATE temp a
INNER JOIN
(
SELECT name, COUNT(*) AS name_count
FROM temp
GROUP BY name
) b
ON a.name = b.name
SET a.name_count = b.name_count;
i have data below for example
id product_id date
------ ---------- ----
1 1 1
2 1 2
3 1 3
4 2 1
5 2 2
6 2 2
7 3 1
result data query that i want "the last record of last date on each product_id"
to get it that result i use the query like below
SELECT a.* FROM test AS a
JOIN (SELECT MAX(id) AS id, product_id, MAX(DATE) AS DATE FROM test GROUP BY product_id) AS b
ON a.id = b.id AND a.product_id = b.product_id AND a.date = b.date
this time i got what i want as the result
id product_id date
------ ---------- --------
3 1 3
6 2 2
7 3 1
my problem when i add another data like below
id product_id date
------ ---------- --------
1 1 1
2 1 2
3 1 3
4 2 1
5 2 2
6 2 2
7 3 1
8 1 3
9 1 2
and use the same query the result become like this
id product_id date
------ ---------- --------
6 2 2
7 3 1
where the the value '1' for product_id?
Try this
SELECT id, product_id, DATE FROM test sitem WHERE product_id IN (1,2,3) AND DATE = (SELECT DATE FROM test WHERE product_id =
sitem.product_id ORDER BY DATE DESC LIMIT 1) AND id =
(SELECT id FROM test WHERE product_id = sitem.product_id ORDER BY DATE DESC,
id DESC LIMIT 1) GROUP BY product_id
This is your subquery:
SELECT MAX(id) AS id, product_id, MAX(DATE) AS DATE
FROM test
GROUP BY product_id
It is independently calculating the maximum of id and date. But, there is no guarantee that these two values are in the same record. There are ways to fix the subquery, but they are rather complicated.
Instead, I would suggest using an alternative method to get the last record:
SELECT t.*
FROM test t
WHERE NOT EXISTS (SELECT 1
FROM test t2
WHERE t2.product_id = t.product_id AND
(t2.date > t.date OR
t2.date = t.date AND t2.id > t.id
);
This identifies the last record for each product as the one where no other record has a larger date. And, if two records have the same date, no other record has a larger id.
I am writing a query to grab the items that a specific user_id was the first to use. Here is some sample data -
item_id used_user_id date_used
1 1 2012-08-25
1 2 2012-08-26
1 3 2012-08-27
2 2 2012-08-27
3 1 2012-08-27
4 1 2012-08-21
4 3 2012-08-24
5 3 2012-08-23
query
select item_id as inner_item_id, ( select used_user_id
from test
where test.item_id = inner_item_id
order by date_used asc
limit 1 ) as first_to_use_it
from test
where used_user_id = 1
group by item_id
It returns the correct values
inner_item_id first_to_use_it
1 1
3 1
4 1
but the query is VERY slow on a giant table. Is there a certain index that I can use or a better query that I can write?
i can't get exactly what you mean because in your inner query you have sorted it by their used_user_id and and on your outer query you have filtered it also by their userid. Why not do this directly?
SELECT DISTINCT item_id AS inner_item_id,
used_user_id AS first_to_use_it
FROM test
WHERE used_user_id = 1
UPDATE 1
SELECT b.item_id,
b.used_user_id AS first_to_use_it
FROM
(
SELECT item_ID, MIN(date_used) minDate
FROM tableName
GROUP BY item_ID
) a
INNER JOIN tableName b
ON a.item_ID = b.item_ID AND
a.minDate = b.date_used
WHERE b.used_user_id = 1