Simplified for example, I have two tables, groups and items.
items (
id,
groupId,
title
)
groups (
id,
groupTitle,
externalURL
)
The regular query I'm goes something like this:
SELECT
i.`id`,
i.`title`,
g.`id` as 'groupId',
g.`groupTitle`,
g.`externalURL`
FROM
items i INNER JOIN groups g ON (i.`groupId` = g.`id`)
However I need to modify this now, because all the groups which specify an externalURL will not have any corresponding records in the items table (since they're stored externally). Is it possible to do some sort of join so that the output looks kinda like this:
items:
id title groupId
----------------------
1 Item 1 1
2 Item 2 1
groups
id groupTitle externalURL
-------------------------------
1 Group 1 NULL
2 Group 2 something
3 Group 3 NULL
Query output:
id title groupId groupTitle externalURL
---------------------------------------------------
1 Item 1 1 Group 1 NULL
2 Item 2 1 Group 1 NULL
NULL NULL 2 Group 2 something
-- note that group 3 didn't show up because it had no items OR externalURL
Is that possible in one SQL query?
This is exactly what an outer join is for: return all the rows from one table, whether or not there is a matching row in the other table. In those cases, return NULL for all the columns of the other table.
The other condition you can take care of in the WHERE clause.
SELECT
i.`id`,
i.`title`,
g.`id` as 'groupId',
g.`groupTitle`,
g.`externalURL`
FROM
items i RIGHT OUTER JOIN groups g ON (i.`groupId` = g.`id`)
WHERE i.`id` IS NOT NULL OR g.`externalURL` IS NOT NULL;
Only if both i.id and g.externalURL are NULL, then the whole row of the joined result set should be excluded.
Related
Would it be possible to add more rows base on Keyword string in SQL ?
table A
PID PromotionName
1 OUT_EC_D10_V500K_FamilyCare_PROCO
2 OUT_EC_D5_V50K_Lunchbox_PROCO
3 OUT_EC_D5_V50K_PROCO
table B
promotion_code itm_name quantity
Lunchbox Item name 1 1
FamilyCare Item name 2 1
FamilyCare Item name 3 1
BUY1FREE6 Item name 4 1
HiSummer Item name 5 1
FamilyCare Item name 6 1
Example:
SELECT * FROM A where pid = '1';
Output of the SQL should be -
PID PromotionName Itm_name quantity
1 OUT_EC_D10_V500K_FamilyCare_PROCO
2 FamilyCare Item name 2 1
3 FamilyCare Item name 3 1
4 FamilyCare Item name 6 1
How to find string with keyword 'FamilyCare' in PromotionName of table A base on promotion_code of table B? If it exist it will add more rows in output
Any help with the SQL?
Here is how you can achieve this:
SELECT PID,PromotionName, '' as Itm_name, NULL as quantity
FROM A
WHERE pid = '1'
UNION
SELECT PID, PROMOTION_NAME, Itm_name, quantity
FROM
(SELECT * FROM A inner join B on a.promotionName LIKE '%'||b.promotion_name||'%')
WHERE pid='1'
You have to update your pid in both the places (before and after UNION).
Notice that tables were joined using LIKE operator with % before and after the word. Hence this joins if a part of a string is present in another column.
db<>fiddle link here
An option would be starting to construct a subquery factoring along with joining tables through a.promotionName LIKE '%'||b.promotion_code||'%' condition while filtering by b.promotion_code = 'FamilyCare', then add another query to combine the result sets by UNION ALL, and then enumerate with an id column by ROW_NUMBER() analytic function such as
WITH ab AS
(
SELECT a.*, b.*
FROM a
JOIN b
ON a.promotionName LIKE '%'||b.promotion_code||'%'
WHERE b.promotion_code = 'FamilyCare'
), ab2 AS
(
SELECT promotion_code, itm_name, quantity
FROM ab
UNION ALL
SELECT DISTINCT promotionName, NULL, NULL
FROM ab
)
SELECT ROW_NUMBER() OVER (ORDER BY itm_name NULLS FIRST) AS pid,
a.*
FROM ab2 a
if there's mismatch for the topmost query, then no row will be returned. eg. that query will check for the existence for the literal you provide
Demo
I need to find the rows in one table that meet specific attributes specified in a foreign key table.
I have these two tables:
ITEM
PK: ItemId
Text: nvarchar
ITEMATTRIBUTE
PK: ItemAttributeId
FK: ItemId
AttributeText: nvarchar
Value: int
ItemAttribute has a foreign key to Items and defines dynamic attributes given for an item.
e.g:
ITEM:
ItemId Text
1 ItemA
2 ItemB
3 ItemC
ITEMATTRIBUTE:
ItemAttributeID ItemId AttributeText Value
1 1 AttributeA 10
2 1 AttributeB 10
3 2 AttributeA 8
I need to dynamically find items which have certain itamAttributes.
For example the desired query shall return items that have
AttributeA AND AttributeB: result should show only ItemA.
When I (left) join both tables I get a row for each item with the joined itemattribute:
select * from item i left join itemattribute a on i.itemid=a.itemid
However I need a dynamic way to get items where defined itemattributes are set:
get all items that have AttributeA with a value > 5 and AttributeB with value > 5: result ItemA
As I don't know how many itemAttributes are set I can't do the query with stacked subselects or hardcoded as in:
select distinct i2.itemid from item i2, itemattribute a2,
(select i.itemid, a.attributetext from item i left join itemattribute a on i.itemid=a.itemid where AttributeText='AttributeA' and value > 5) ii
where i2.itemid=a2.itemid and a2.attributetexT='AttributeB' and value > 5
You need to aggregate your values to the Item level, then do the logic to filter for the Items you want.
In some dbs (like Snowflake) you can run a PIVOT, but in most you need to do conditional aggregations.
SELECT item_id, att_a_value, att_b_value
FROM (
SELECT
i.item_id
,max(CASE WHEN ia.AttributeText = 'Attribute A' THEN ia.value END) as att_a_value
,max(CASE WHEN ia.AttributeText = 'Attribute B' THEN ia.value END) as att_b_value
FROM Items i
LEFT JOIN ItemAttributes ia ON i.item_id = ia.item_id
GROUP BY i.item_id
) z
WHERE z.att_a_value > 5 AND z.att_b_value > 5
database table like this
============================
= suburb_id | value
= 1 | 2
= 1 | 3
= 2 | 4
= 3 | 5
query is
SELECT COUNT(suburb_id) AS total, suburb_id
FROM suburbs
where suburb_id IN (1,2,3,4)
GROUP BY suburb_id
however, while I run this query, it doesn't give COUNT(suburb_id) = 0 when suburb_id = 0
because in suburbs table, there is no suburb_id 4, I want this query to return 0 for suburb_id = 4, like
============================
= total | suburb_id
= 2 | 1
= 1 | 2
= 1 | 3
= 0 | 4
A GROUP BY needs rows to work with, so if you have no rows for a certain category, you are not going to get the count. Think of the where clause as limiting down the source rows before they are grouped together. The where clause is not providing a list of categories to group by.
What you could do is write a query to select the categories (suburbs) then do the count in a subquery. (I'm not sure what MySQL's support for this is like)
Something like:
SELECT
s.suburb_id,
(select count(*) from suburb_data d where d.suburb_id = s.suburb_id) as total
FROM
suburb_table s
WHERE
s.suburb_id in (1,2,3,4)
(MSSQL, apologies)
This:
SELECT id, COUNT(suburb_id)
FROM (
SELECT 1 AS id
UNION ALL
SELECT 2 AS id
UNION ALL
SELECT 3 AS id
UNION ALL
SELECT 4 AS id
) ids
LEFT JOIN
suburbs s
ON s.suburb_id = ids.id
GROUP BY
id
or this:
SELECT id,
(
SELECT COUNT(*)
FROM suburb
WHERE suburb_id = id
)
FROM (
SELECT 1 AS id
UNION ALL
SELECT 2 AS id
UNION ALL
SELECT 3 AS id
UNION ALL
SELECT 4 AS id
) ids
This article compares performance of the two approaches:
Aggregates: subqueries vs. GROUP BY
, though it does not matter much in your case, as you are querying only 4 records.
Query:
select case
when total is null then 0
else total
end as total_with_zeroes,
suburb_id
from (SELECT COUNT(suburb_id) AS total, suburb_id
FROM suburbs
where suburb_id IN (1,2,3,4)
GROUP BY suburb_id) as dt
#geofftnz's solution works great if all conditions are simple like in this case. But I just had to solve a similar problem to generate a report where each column in the report is a different query. When you need to combine results from several select statements, then something like this might work.
You may have to programmatically create this query. Using left joins allows the query to return rows even if there are no matches to suburb_id with a given id. If your db supports it (which most do), you can use IFNULL to replace null with 0:
select IFNULL(a.count,0), IFNULL(b.count,0), IFNULL(c.count,0), IFNULL(d.count,0)
from (select count(suburb_id) as count from suburbs where id=1 group by suburb_id) a,
left join (select count(suburb_id) as count from suburbs where id=2 group by suburb_id) b on a.suburb_id=b.suburb_id
left join (select count(suburb_id) as count from suburbs where id=3 group by suburb_id) c on a.suburb_id=c.suburb_id
left join (select count(suburb_id) as count from suburbs where id=4 group by suburb_id) d on a.suburb_id=d.suburb_id;
The nice thing about this is that (if needed) each "left join" can use slightly different (possibly fairly complex) query.
Disclaimer: for large data sets, this type of query might have not perform very well (I don't write enough sql to know without investigating further), but at least it should give useful results ;-)
I need a SQL statement to retrieve records where it key (or any column) is in a associate table, for example:
documentId termId
4 1
4 2
3 3
5 1
This:
SELECT documentId
FROM table
WHERE termId IN (1,2,3)
...will retrieve any documentid value where the termid value is 1 or 2 or 3.
Is there something like this but return documentid values where the termid values are 1 and 2 and 3? Like an IN but with AND.
There's no straight forward functionality, but there are two options:
Using GROUP BY/HAVING
SELECT t.documentid
FROM TABLE t
WHERE t.termid IN (1,2,3)
GROUP BY t.documentid
HAVING COUNT(DISINCT t.termid) = 3
The caveat is that you have to use HAVING COUNT(DISTINCT because duplicates of termid being 2 for the same documentid would be a false positive. And the COUNT has to equal the number of termid values in the IN clause.
Using JOINs
SELECT t.documentid
FROM TABLE t
JOIN TABLE x ON x.termid = t.termid
AND x.termid = 1
JOIN TABLE y ON y.termid = t.termid
AND y.termid = 2
JOIN TABLE z ON z.termid = t.termid
AND z.termid = 3
But this one can be a pain for handling criteria that changes a lot.
I have a table in my database:
Name | Element
1 2
1 3
4 2
4 3
4 5
I need to make a query that for a number of arguments will select the value of Name that has on the right side these and only these values.
E.g.:
arguments are 2 and 3, the query should return only 1 and not 4 (because 4 also has 5). For arguments 2,3,5 it should return 4.
My query looks like this:
SELECT name FROM aggregations WHERE (element=2 and name in (select name from aggregations where element=3))
What do i have to add to this query to make it not return 4?
A simple way to do it:
SELECT name
FROM aggregations
WHERE element IN (2,3)
GROUP BY name
HAVING COUNT(element) = 2
If you want to add more, you'll need to change both the IN (2,3) part and the HAVING part:
SELECT name
FROM aggregations
WHERE element IN (2,3,5)
GROUP BY name
HAVING COUNT(element) = 3
A more robust way would be to check for everything that isn't not in your set:
SELECT name
FROM aggregations
WHERE NOT EXISTS (
SELECT DISTINCT a.element
FROM aggregations a
WHERE a.element NOT IN (2,3,5)
AND a.name = aggregations.name
)
GROUP BY name
HAVING COUNT(element) = 3
It's not very efficient, though.
Create a temporary table, fill it with your values and query like this:
SELECT name
FROM (
SELECT DISTINCT name
FROM aggregations
) n
WHERE NOT EXISTS
(
SELECT 1
FROM (
SELECT element
FROM aggregations aii
WHERE aii.name = n.name
) ai
FULL OUTER JOIN
temptable tt
ON tt.element = ai.element
WHERE ai.element IS NULL OR tt.element IS NULL
)
This is more efficient than using COUNT(*), since it will stop checking a name as soon as it finds the first row that doesn't have a match (either in aggregations or in temptable)
This isn't tested, but usually I would do this with a query in my where clause for a small amount of data. Note that this is not efficient for large record counts.
SELECT ag1.Name FROM aggregations ag1
WHERE ag1.Element IN (2,3)
AND 0 = (select COUNT(ag2.Name)
FROM aggregatsions ag2
WHERE ag1.Name = ag2.Name
AND ag2.Element NOT IN (2,3)
)
GROUP BY ag1.name;
This says "Give me all of the names that have the elements I want, but have no records with elements I don't want"