Reuse When condition in result query - sql

Question

I did this query and it works but it is possible to do something more efficient and readable ? I just want to have a result in a query (I don't want to use pl/sql for this). The best would be to store the when condition in a variable but I don't know if it is possible.
SELECT
CASE WHEN (SELECT min(handling_unit_id) FROM ifsapp.handling_unit_shipment where
shipment_id = '1371'
AND ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(handling_unit_type_id) like 'SST_N1'
and structure_level = 1) is not null
THEN (SELECT min(handling_unit_id) FROM ifsapp.handling_unit_shipment where
shipment_id = '1371'
AND ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(handling_unit_type_id) like 'SST_N1'
and structure_level = 1)
ELSE (SELECT min(handling_unit_id) FROM ifsapp.handling_unit_shipment where
shipment_id = '1371'
AND ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(handling_unit_type_id) like 'SST_N1'
and structure_level > 1)
END HUI FROM dual ;

Answer 1

You may use a below query (if you want a single value as in the current example):
select handling_unit_id
from ifsapp.handling_unit_shipment
where shipment_id = '1371'
and ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(
handling_unit_type_id
) like 'SST_N1'
and structure_level >= 1
order by structure_level asc, handling_unit_id asc
fetch first row only
What will it do:
It orders the data by structure_level in ascending order, so given structure_level >= 1 will return structure_level = 1 as a first row if it is present and structure_level > 1 if it is not.
If there are many handling_unit_id per structure value, then it will put the least handling_unit_id at the first row, which is an equivalent of min.

Answer 2

You could make it a little more compact using the coalesce function
SELECT coalesce(
(SELECT min(handling_unit_id) FROM ifsapp.handling_unit_shipment where
shipment_id = '1371'
AND ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(handling_unit_type_id) like 'SST_N1'
and structure_level = 1),
(SELECT min(handling_unit_id) FROM ifsapp.handling_unit_shipment where
shipment_id = '1371'
AND ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(handling_unit_type_id) like 'SST_N1'
and structure_level > 1)
)
FROM dual ;
The coalesce function basically returns the first not null value among its input parameters

Answer 3

You may use query factoring or common-table-expression.
with tb as (
SELECT min(handling_unit_id) min_hu_id
FROM ifsapp.handling_unit_shipment
where shipment_id = '1371'
AND ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(handling_unit_type_id) like 'SST_N1'
and structure_level = 1)
)
select coalesce(min_hu_id
,(SELECT min(handling_unit_id)
FROM ifsapp.handling_unit_shipment
where shipment_id = '1371'
AND ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(handling_unit_type_id) like 'SST_N1'
and structure_level > 1)
from tb
;

Answer 4

Another option. Figure out what is common to all three queries and do it once in a CTE (WITH clause). Then query that in respective ways to look for what is different in each case. Then there are various modes of doing the CASE/IF-THEN type logic. Here's one means. It uses a tricky SIGN operation in order to group all the >1 structure_level values together.
WITH data AS (SELECT SIGN(structure_level-1)+1 structure_level_group,min(handling_unit_id) min_handling_unit_id
FROM ifsapp.handling_unit_shipment
WHERE shipment_id = '1371'
AND ifsapp.HANDLING_UNIT_TYPE_API.Get_Handling_Unit_Category_Id(handling_unit_type_id) like 'SST_N1'
GROUP BY SIGN(structure_level-1)+1)
SELECT NVL(t1.min_handling_unit_id,t2.min_handling_unit_id) hui
FROM (SELECT MIN(min_handling_unit_id) min_handling_unit_id
FROM data
WHERE structure_level_group = 1) t1,
(SELECT MIN(min_handling_unit_id) min_handling_unit_id
FROM data
WHERE structure_level_group = 2) t2