SQL Error Converting Data to Int When I am Not Asking It To - sql

Question

I have the following SQL statement. In it I need to convert some numbers stored as varchar to decimal in order to sum them.
When I run this SQL against my constraints I get this message:
Msg 245, Level 16, State 1, Line 1
Conversion failed when converting the varchar value '1635.34' to data
type int.
Which baffles me because I am casting my data as decimal. It also baffles me because when I use different constraints that have the same type of data in the field (1234.56 type of format) it works. That data is in the TotalPremium field.
(My logic is a bit complex so that is why SQL statement is complex. I am posting all of it for clarity sake. Also, redesigning database table field type is not an option at this point.)
SELECT Account_No, version_num, LineOfBus, ProductNo, QuoteNo, Sum(Cast(TotalPremium as Decimal(16,2))) TotalPremium
FROM
(SELECT t.Account_No, t.version_num,
CASE
WHEN t.PackageIndicator = '1' THEN 'Package' Else t.Lob
END AS LineOfBus,
t.ProductNo, t.QuoteNo, Cast(COALESCE(t.TotalPremium,0) as decimal(16,2)) TotalPremium
FROM uAccountProductInfo as T
WHERE t.version_num IN
(SELECT sqVersionNumber.version_num
FROM
/* this captures unique package product records (or just stand alone records as well) */
(SELECT DISTINCT sqUnique.version_num, Count(sqUnique.version_num) VersionCount
FROM
/* grab list of all uniquer version, product, quote combinations (use distinct to combine package */
(SELECT DISTINCT version_num, productNo, quoteNo
FROM uAccountProductInfo
WHERE Account_No = '1172014' /* pass as parameter */
AND ProductNo IN ('6472930', '6474927') /* pass as parameter */
AND QuoteNo IN ('724185-01', '881957-08') /* pass as parameter */
) AS sqUnique
GROUP BY version_num
HAVING Count(version_num) = 2 /* pass as variable based on number of products, quotes */
) as sqVersionNumber
)
AND t.Account_no = '1172014' /* pass as parameter */
AND t.ProductNo IN ('6472930', '6474927') /* pass as parameter */
AND t.QuoteNo IN ('724185-01', '881957-08') /* pass as parameter */) as sqLOB
GROUP BY Account_No, version_num, LineOfBus, ProductNo, QuoteNo

Answer 1

The problem is that SQL Server does not guarantee the order of evaluation of operations. You clearly have something improper in the field. In SQL Server 2012+, use try_convert():
SELECT Sum(try_convert(decimal(16, 2), TotalPremium ))) as TotalPremium
In earlier versions, use case:
SELECT Sum(case when isnumeric(TotalPremium) = 1 then convert(decimal(16, 2), TotalPremium)) end) as TotalPremium
isnumeric() is not perfect, but it should be good enough for your purposes.

Answer 2

Cast t.TotalPremium to decimal before coalescing. Your query is doing coalesce on a string and an integer, then casting the result to decimal. Try using0.0instead of0as well.
edit I do not actually think using 0.0 rather than 0 is a good idea, aside from readability. If that is the goal, cast it to the same decimal datatype. Otherwise, this could be construed as a datatype dominant over decimal. 0 as int or varchar should not take precedence over our value casted to a decimal.

Answer 3

You could use isnull() instead of coalesce(), though it would still be better practice to use the same datatype as RexMaison points out.
create table t (TotalPremium varchar(16));
insert into t values (''),(null),('1635.34');
/* no error */
select isnull(t.TotalPremium,0)
from t;
/* no error */
select coalesce(t.TotalPremium,'0')
from t;
/* error */
select coalesce(t.TotalPremium,0)
from t;
rextester demo: http://rextester.com/OHEJ71310

Answer 4

Just posting final code that worked after incorporating elements of all 3 answers.
SELECT Account_No, version_num, LineOfBus, ProductNo, QuoteNo,
SUM(CASE
WHEN ISNUMERIC(TotalPremium) = 1 THEN CONVERT(decimal(16,2),TotalPremium)
END) As TotalPremium
FROM
(SELECT t.Account_No, t.version_num,
CASE
WHEN ISNull(t.PackageIndicator,'0') = '1' THEN 'Package' Else t.Lob
END AS LineOfBus,
t.ProductNo, t.QuoteNo,
ISNull(CASE
WHEN ISNUMERIC(t.TotalPremium) = 1 THEN CONVERT(decimal(16,2),t.TotalPremium)
END, 0) TotalPremium
FROM uAccountProductInfo as T
WHERE t.version_num IN
(SELECT sqVersionNumber.version_num
FROM
/* this captures unique package product records (or just stand alone records as well) */
(SELECT DISTINCT sqUnique.version_num, Count(sqUnique.version_num) VersionCount
FROM
/* grab list of all uniquer version, product, quote combinations (use distinct to combine package */
(SELECT DISTINCT version_num, productNo, quoteNo
FROM uAccountProductInfo
WHERE Account_No = '1172014' /* pass as parameter */
AND ProductNo IN ('6472930', '6474927') /* pass as parameter */
AND QuoteNo IN ('724185-01', '881957-08') /* pass as parameter */
) AS sqUnique
GROUP BY version_num
HAVING Count(version_num) = 2 /* pass as variable based on number of products, quotes */
) as sqVersionNumber
)
AND t.Account_no = '1172014' /* pass as parameter */
AND t.ProductNo IN ('6472930', '6474927') /* pass as parameter */
AND t.QuoteNo IN ('724185-01', '881957-08') /* pass as parameter */) as sqLOB
GROUP BY Account_No, version_num, LineOfBus, ProductNo, QuoteNo