I am currently retrieving data from multiple tables using a cus_id as the initial query. From here I have multiple tables that can have various rows of data that I would like to retrieve and use GROUP_CONCAT to return this data in a single row. At the moment, my query is returning duplicate data based on the max number of rows returned by one of the group concats.
SELECT a.id,c.x,c.y,c.z
GROUP_CONCAT(a.column_a) AS aca,
GROUP_CONCAT(a.column_b) AS acb,
GROUP_CONCAT(b.column_a) AS bca,
GROUP_CONCAT(b.column_b) AS bcb,
FROM `table_a` a
INNER JOIN `table_b` b ON a.id = b.id
INNER JOIN `table_c` c ON a.id = c.id
WHERE a.id = ?
Also, in this scenario, what is the correct join method to use. I am expecting all the fields I am requesting to have some sort of data.
Problem was resolved by using sub queries to isolate the GROUP_CONCAT requests. This allowed me to get only the data I wanted without duplicate results manipulated by other JOIN requests.
SELECT a.id,c.x,c.y,c.z
(SELECT GROUP_CONCAT(column_a) FROM table_a) AS aca,
(SELECT GROUP_CONCAT(column_b) FROM table_a) AS acb,
(SELECT GROUP_CONCAT(column_a) FROM table_b) AS bca,
(SELECT GROUP_CONCAT(column_b) FROM table_b) AS bcb,
FROM table_a a
INNER JOIN `table_c` c ON a.id = c.id
WHERE a.id = ?
Aggregate before joining. Somthing along the lines of:
select
a.*,
b.grp_a,
b.grp_b,
c.grp_x,
b.grp_y
from table_a a
join
(
select
a_id,
group_concat(a order by b_id) as grp_a,
group_concat(b order by b_id) as grp_b
from table_b
group by a_id
) b on b.a_id = a.id
join
(
select
a_id,
group_concat(x order by c_id) as grp_x,
group_concat(y order by c_id) as grp_y
from table_c
group by a_id
) c on c.a_id = a.a_id
order by a.a_id;
Related
I have a SQL statement that does left join with a table:
select a.id, b.col1 from tableA a
left join (select col1 from tableB where date = 'xxx') b on a.id = b.id
For some application constraint (I need to use Spring JPQL query that does not permit subquery), I need to "flatten" this query to remove the subquery without changing the meaning of the query: I want to enrich tableA with a subset of tableB.
I have tried a few queries such as:
select a.id, b.col1 from tableA a
left join tableB b on a.id = b.id
where (date = 'xxx' or date is null)
But that gave me different set of answer from previous query.
How do I remove this subquery?
It can be done in multiple different ways - using cte, using joins
Using join it can be implemented as -
select a.id, b.col1 from tableA a left join tableB b on a.id = b.id and b.date = 'xxx'
using CTE it can be implemented as -
with t as
(
select col1, id from tableB where date = 'xxx'
)
select a.id, b.col1 from tableA a
left join t on a.id = t.id
I have 2 tables in my SQL database. Let's call them Table A and Table B.
I have joined both the tables using left join on ID = AID. Table A has a field by name ID and Table B has field AID and Price.
The problem is Table B can have multiple prices for the ID present in Table A.
The requirement is - If only one price is present in Table B corresponding to ID in table A then it should return that price.
If more than one price is present in table B for an ID in table A then I should get the price as Zero/null.
Query -
SELECT DISTINCT A.ID,B.Price
from A
left join B
on A.ID = B.AID
where "some condition"
Use Count() with Over() window function to find the count of records for each ID then based on count return the price
Try this way
SELECT DISTINCT A.ID,
case when count(1) over(partition by A.ID) > 1 then NULL else B.Price end
from A
left join B
on A.ID = B.AID
For Mysql
SELECT DISTINCT a.id,
CASE
WHEN c.aid IS NULL THEN NULL
ELSE b.price
END
FROM a
LEFT JOIN b
ON a.id = b.aid
LEFT JOIN (SELECT aid
FROM b
GROUP BY aid
HAVING Count(1) = 1) c
ON a.id = c.aid
For SQL Server (should work for MySQL too). One sub-query (you can put in CTE) that shows only AIDs that have only one price:
SELECT A.ID,
B.Price
FROM A
LEFT JOIN (
SELECT AID
FROM B
GROUP BY AID
HAVING COUNT(Price) = 1
) as C
ON C.AID = A.ID
LEFT JOIN B
ON C.AID = B.AID
Use below query. It should work.
SELECT A.ID, o.Price
FROM A
OUTER APPLY
(
SELECT IIF(COUNT(B.Price)>1,NULL,MAX(B.Price)) AS Price
FROM B
WHERE B.AID = A.ID
) AS o;
SELECT *
FROM table_a
LEFT JOIN table_b ON (table_b.id = table_a.id)
WHERE table_b.created BETWEEN ? AND ?
AND table_b.manager IN(
SELECT DISTINCT (b.id)
FROM table_b a
INNER JOIN table_b b ON a.manager = b.id
AND b.user_level > 0
AND b.id != 1
)
How can I remove the sub query and use JOINS instead in the above query
Thanks
MySQL 5.5 (and lower version)'s optimizer produces a DEPENDENT SUBQUERY for IN (SELECT ...) which means every matching row is found, IN(SELECT ...) is evaluated that makes select slow.
Simple optimization of your query is make inline view as follows:
SELECT *
FROM table_a LEFT JOIN table_b ON (table_b.id = table_a.id)
INNER JOIN (
SELECT DISTINCT b.id AS id
FROM table_b a
INNER JOIN table_b b ON a.manager = b.id
AND b.user_level > 0
AND b.id != 1
) x ON table_b.manager = x.id
WHERE table_b.created BETWEEN ? AND ?
AND x.id IS NOT NULL;
I think avobe query would produce as same as your own.
Last, DISTINCT is not a function. please use SELECT DISTINCT b.id rather SELECT DISTINCT (b.id)
Consider the following schema:
create table A
(
id int primary id
)
create table B
(
a_id int,
s varchar(255)
)
And then the following query:
select A.id, sum(1), ??? concat_join(B.s) ???
from A left join B on A.id = B.a_id group by A.id
There is a 1-to-many relation between A and B, so multiple rows will be grouped into one. The desired behaviour of "concat_join" would be for each B.s in the group join them together into a single string by concatenating them (perhaps with a space seperator).
Is there someway to express this is MySQL 5.5?
use GROUP_CONCAT
select A.id, sum(1), GROUP_CONCAT(B.s)
from A left join B on A.id = B.a_id
group by A.id
by default, the string is separated by a comma. if you want to change it, add SEPARATOR keyword,
select A.id, sum(1), GROUP_CONCAT(B.s SEPARATOR ';')
from A left join B on A.id = B.a_id
group by A.id
SQLFiddle Demo
So I have two tables like this:
create table A
{
id int;
...
}
create table B
{
id int;
a_id int;
t timestamp;
...
}
A is one-to-many with B
I want to:
SELECT * FROM A LEFT JOIN B ON A.id = B.a_id ???
But I want to return exactly one row for each entry in A which has the B with the newest t field (or null for Bs fields if it has no B entry).
That is rather than returning all A-B pairs, I want to only select the newest one with respect to A (or A-null if no B entry).
Is there some way to express this in SQL? (I'm using MySQL 5.5)
LEFT JOIN is only concerned with ensuring every row in A is returned, even if there is no corresponding joined row in B.
The need for just one row needs another condition. MySQL is limitted in its options, but one could be:
SELECT
*
FROM
A
LEFT JOIN
B
ON B.id = A.id
AND B.t = (SELECT MAX(lookup.t) FROM B AS lookup WHERE lookup.id = A.id)
Another could be...
SELECT
*
FROM
A
LEFT JOIN
(
SELECT id, MAX(t) AS t FROM B GROUP BY id
)
AS lookup
ON lookup.id = A.id
LEFT JOIN
B
ON B.id = lookup.id
AND B.t = lookup.t
You could do the following:
SELECT A.*, B.*
FROM
A
LEFT JOIN
(SELECT B.a_id, MAX(t) as t FROM B GROUP BY B.a_id) BMax
ON A.id = BMax.a_id
JOIN B
ON B.a_id = BMax.a_id AND B.t = BMax.t
you first need to get the newest t from tableB in a subquery, then join it with tableA and tableB.
SELECT a.*, c.*
FROM tableA a
LEFT JOIN
(
SELECT a_ID, max(t) maxT
FROM tableB
GROUP BY a_ID
) b on a.a_id = b.a_ID
LEFT JOIN tableB c
ON b.a_ID = c.a_ID AND
b.maxT = c.t
try this:
SELECT *
FROM tableA A LEFT JOIN
(select a_id ,max(t) as max_t
from tableB
group by a_id )b
on A.id = b.a_id
and A.t=b.max_t