Get rows with multiple conditions - sql

Question

Below is my Postgres table:
Table:
+------+-----------------+---------+
| sku | properties | value |
|------+-----------------+---------|
| 1 | Family_ID | 21 |
| 1 | Class_ID | 21 |
| 2 | Family_ID | 20 |
| 2 | Class_ID | 21 |
| 3 | Family_ID | 21 |
| 3 | Class_ID | 21 |
+------+-----------------+---------+
How to query if I want to fetch data where the Family_ID and Class_ID is 21.
The expected return value:
+------+-----------------+---------+
| sku | properties | value |
|------+-----------------+---------|
| 1 | Family_ID | 21 |
| 1 | Class_ID | 21 |
| 3 | Family_ID | 21 |
| 3 | Class_ID | 21 |
+------+-----------------+---------+
How to query if I want to fetch data where the Family_ID is 20 and Class_ID is 21.
The expected return value:
+------+-----------------+---------+
| sku | properties | value |
|------+-----------------+---------|
| 2 | Family_ID | 20 |
| 2 | Class_ID | 21 |
+------+-----------------+---------+

Answer 1

This query:
select sku
from tablename
group by sku
having
max(case when properties = 'Family_ID' then value end) = 21
and
max(case when properties = 'Class_ID' then value end) = 21
returns all the skus that satisfy your conditions and you can use it with the operator IN like this:
select * from tablename
where sku in (
select sku
from tablename
group by sku
having
max(case when properties = 'Family_ID' then value end) = 21
and
max(case when properties = 'Class_ID' then value end) = 21
)
You could also use MAX() window function:
select t.sku, t.properties, t.value
from (
select *,
max(case when properties = 'Family_ID' then value end) over (partition by sku) family_id,
max(case when properties = 'Class_ID' then value end) over (partition by sku) class_id
from tablename
) t
where t.family_id = 21 and t.class_id = 21
See the demo.
Results:
> sku | properties | value
> --: | :--------- | ----:
> 1 | Family_ID | 21
> 1 | Class_ID | 21
> 3 | Family_ID | 21
> 3 | Class_ID | 21

Answer 2

To operate across rows you need to group, but the easiest thing here (given that you seem like you will want ever more variations of this theme) is probably to pivot your data:
WITH x as(
SELECT f.sku, c.value as class_value, f.value as family_value
FROM
(select sku, value FROM table WHERE properties = 'family_id') f
INNER JOIN
(select sku, value FROM table WHERE properties = 'class_id') c
ON f.sku = c.sku
)
You can now use a WHERE clause like normal:
SELECT * FROM x WHERE family_value = 20 and class_value = 21
If you need the data back in a column format, you can unpivot it again:
SELECT
sku,
'family_id' as properties,
family_value as value
FROM
x
UNION ALL
SELECT
sku,
'class_id' as properties,
class_value as value
FROM
x
But it might be easier to just work with the data in its pivoted form.
I wouldn't necessarily do this myself, but its a lot easier to understand this form of pivoting if you're used to regular joining, union and other similar "typical" database operations, so I'm recommending this as you may well find it easier to maintain and extend. Conditional aggregation to do a pivot is potentially more efficient but more complex to maintain:
WITH X as (
SELECT
sku,
MAX(CASE WHEN properties = 'Family_ID' THEN value END) as family_value,
MAX(CASE WHEN properties = 'Class_ID' THEN value END) as class_value
FROM
table
GROUP BY sku
)
The CASE WHENs spread the values across columns according to the properties value. The group by/max then collapse the rows removing the nulls leaving you with a unique sku and the values in named columns according to what kind of value they are

Answer 3

--case 1
select *
from tbl t
where exists (select *
from tbl t1
where t1.sku=t.sku
and t1.properties='Family_ID'
and t1.value=21)
and exists (select *
from tbl t1
where t1.sku=t.sku
and t1.properties='Class_ID'
and t1.value=21)
--case 2
select *
from tbl t
where exists (select *
from tbl t1
where t1.sku=t.sku
and t1.properties='Family_ID'
and t1.value=20)
and exists (select *
from tbl t1
where t1.sku=t.sku
and t1.properties='Class_ID'
and t1.value=21)