MSSQL 2012 - Why is AVG & TRY_CONVERT not returning the correct value? - sql

Question

I am using MSSQL 2012 and I am trying to use AVG together with TRY_CONVERT on a table column with the following datatype: nvarchar(255), NOT NULL
First before I try to query using AVG & TRY_CONVERT, this is the data that I want to get the AVG value out of using this query:
And this is the results after using AVG and TRY_CONVERT, 0 rows returned.
I also tried to use a subquery then i got 18 row returned, but with value NULL, i skipped out on AVG just to see if i was getting the correct values.. but it seems not, i also included the p.serialnumber column to show that its the correct rows that was returned, its just the value NULL that somehow appears after TRY_CONVERT.
UPDATE!:
When I execute the query below which target data that has a "." separator (qtv2.qtv_qteid = 58 (instead of 63)) , it works! So the issue is the "," separator. Anyone know solution to this??
declare #ProjectSelection nvarchar(10)
set #ProjectSelection = 'C82007588'
SELECT AVG(TRY_CONVERT(numeric(10,5), avgcap))
FROM
(
select qtv2.qtv_result as avgcap
from ProductionOrder PO
left join CustomerOrder co on co.CustomerOrderId=po.customerorderid
left join ProductionOrderProperty pop on pop.ProductionOrderId=po.productionorderid
left join product p on p.ProductionOrderId=po.productionorderid
left join QualityTestValues qtv on qtv.qtv_productid=p.ProductId
left join QualityTestValues qtv2 on qtv2.qtv_productId=p.ProductId
where pop.Value=#ProjectSelection and pop.name = 'project' and po.ProductTypeId = 1
and qtv2.qtv_qteid = 58 and qtv2.qtv_valid = 1 and qtv.qtv_ProductSegmentId = 144 and qtv.qtv_valid = 1
and qtv.qtv_qteid = 51 and qtv.qtv_result = 'J'
group by co.CustomerName, pop.Value, qtv2.qtv_result, p.SerialNumber
) A
Result:
(No column name)
22.200000

Answer 1

How about your compatibility level? A similar question can be found here:
TRY_CONVERT fails on SQL Server 2012
Although your server version is 2012, a lower compatibility level can cause the try_convert to be unavailable for use in your database. You can check this by running the following code in your specific database and afterwards on for instance the master database.
DECLARE #b VARCHAR(10) = '12312'
SELECT TRY_CONVERT(INT,#b)

Answer 2

You can take your first query and do something like this:
SELECT AVG(TRY_CONVERT(numeric(10,5), avgcap))
FROM
(
-- Insert your first query here.
) A
This should give you the average of the numbers.
EDIT
Here is a workable example that should return 24.000000.
SELECT AVG(TRY_CONVERT(numeric(10,5), A))
FROM
(
SELECT '22.5' AS A
UNION
SELECT '23.5' AS A
UNION
SELECT '26.0' AS A
) B

Answer 3

I found out the solution, using TRY_PARSE instead of TRY_CONVERT.
DECLARE #ProjectSelection nvarchar(10)
SET #ProjectSelection = 'C82007588'
SELECT AVG(avgcap) as avgcap
FROM
(
SELECT qtv2.qtv_result, TRY_PARSE( qtv2.qtv_result AS NUMERIC(10,3)) avgcap
FROM ProductionOrder PO
LEFT JOIN CustomerOrder co on co.CustomerOrderId=po.customerorderid
LEFT JOIN ProductionOrderProperty pop on pop.ProductionOrderId=po.productionorderid
LEFT JOIN product p on p.ProductionOrderId=po.productionorderid
LEFT JOIN QualityTestValues qtv on qtv.qtv_productid=p.ProductId
LEFT JOIN QualityTestValues qtv2 on qtv2.qtv_productId=p.ProductId
WHERE pop.Value=#ProjectSelection
AND pop.name = 'project'
AND po.ProductTypeId = 1
AND qtv2.qtv_qteid = 63
AND qtv2.qtv_valid = 1
AND qtv.qtv_ProductSegmentId = 144
AND qtv.qtv_valid = 1
AND qtv.qtv_qteid = 51
AND qtv.qtv_result = 'J'
GROUP BY co.CustomerName, pop.Value, qtv2.qtv_result, p.SerialNumber
) A`
Results:
avgcap
21264.850000