How to make multiple row in one column with Case Statement? - sql

Question

I need to join multiple row into one column. I have a table like this.
PRD_ID PRD_CONTAINER CONTAINER_LVL QTY
---------- --------------------- -------------
122 BIG_BOX 4
122 MED_BOX 3 6
122 SML_BOX 2
122 NO_BOX 1 50
All the qty value should be under one column starting with level 4 to 1. If the there is no value for Qty then it should be marked as 0/.
The result I want is like this
PRD_ID QTY
---------- -------
122 0/6/0/50
I tried this
SELECT
PRD_ID,
(CASE WHEN CONTAINER_LVL = 4 AND QTY > 0 THEN dbo.FBE_GetThousandSeparator(QTY,0) ELSE '0/' END +
CASE WHEN CONTAINER_LVL = 3 AND QTY > 0 THEN dbo.FBE_GetThousandSeparator(QTY,0) ELSE '0/' END +
CASE WHEN CONTAINER_LVL = 2 AND QTY > 0 THEN dbo.FBE_GetThousandSeparator(QTY,0) ELSE '0/' END +
CASE WHEN CONTAINER_LVL = 1 AND QTY > 0 THEN dbo.FBE_GetThousandSeparator(QTY,0) ELSE '' END) AS
QTY
FROM
#TMP2
GROUP BY
PRD_ID,
(CASE WHEN CONTAINER_LVL = 4 AND QTY > 0 THEN dbo.FBE_GetThousandSeparator(QTY,0) ELSE '0/' END +
CASE WHEN CONTAINER_LVL = 3 AND QTY > 0 THEN dbo.FBE_GetThousandSeparator(QTY,0) ELSE '0/' END +
CASE WHEN CONTAINER_LVL = 2 AND QTY > 0 THEN dbo.FBE_GetThousandSeparator(QTY,0) ELSE '0/' END +
CASE WHEN CONTAINER_LVL = 1 AND QTY > 0 THEN dbo.FBE_GetThousandSeparator(QTY,0) ELSE '' END)
My result is this:
PRD_ID QTY
---------- -------
122 0/0/0/
122 0/0/0/50
122 0/60/

Answer 1

Per #Larnu's comment, you can use string aggregation. Also, if you're just checking for nulls (rather than concerned with negatives) you don't need case expressions.
select PRD_ID,
string_agg(
convert(nvarchar(32), coalesce(QTY,0))
, '/'
) within group (order by CONTAINER_LVL desc) as QTY
from #TMP
group by PRD_ID
In the above we :
use coalesce to replace any null values with 0s
use convert to change from integers to strings
use string_agg to join all strings together, with / as a delimiter.
use within group (order by CONTAINER_LVL desc) to determine the order the fields are returned in (i.e. the QTY for CONTAINER_LVL=4 first, then 3, etc)
Related documentation: https://learn.microsoft.com/en-us/sql/t-sql/functions/string-agg-transact-sql?view=sql-server-ver16#f-generate-a-sorted-list-of-emails-per-towns
If that's not an option (i.e. as string_agg was only introduced in SQL 2017):
select PRD_ID,
convert(nvarchar(32), coalesce(max(case when CONTAINER_LVL = 4 then QTY end),0))
+ N'/' +
convert(nvarchar(32), coalesce(max(case when CONTAINER_LVL = 3 then QTY end),0))
+ N'/' +
convert(nvarchar(32), coalesce(max(case when CONTAINER_LVL = 2 then QTY end),0))
+ N'/' +
convert(nvarchar(32), coalesce(max(case when CONTAINER_LVL = 1 then QTY end),0))
from #TMP
group by PRD_ID
In the above we:
use the CASE expressions to get the QTY value for the given CONTAINER_LVL value for the given position; for all rows that don't have that CONTAINER_LVL we'd get NULL here. We also get NULL if the QTY value for that CONTAINER_LVL is NULL.
wrap that in MAX so that the multiple row's values (including NULLS) within the group are "squashed"/aggregated down to a single value; in this case the max. If all rows had NULLs, that would be NULL, if we had one numeric value and the rest null (as generally expected) we'd get that numeric value; if we had multiple numeric values (i.e. as we had 2 rows with identical PRD_ID and CONTAINER_LVL values) we'd get the one with the highest QTY value... though I'm assuming this last scenario isn't a valid one, and that you have a unique contraint to protect against it. Note: you could also use SUM here if you wish; then if you have multiple rows with the same PRD_ID and CONTAINER_LVL values their QTYs will be combined for the value at that position.
we wrap that in a coalesce function, such that if the value was NULL we replace that with a 0.
we wrap that in a convert function so we can perfom string concatenation on the value (i.e. '0' + '/' is valid... 0 + '/' is not).
we then use + 'N'/' + between each of these to concatenate the 4 values as expected.
SQL Fiddle Demo

Answer 2

Maybe using PIVOT can solve your problem, try this;
SELECT PROD_ID, [1] AS NO, [2] AS SML, [3] AS MED, [4] AS BIG
FROM #TMP2
PIVOT (
SUM(QTY)
FOR CONTAINER_LVL IN ([1], [2], [3], [4])
) P