Execution plan -warnining with coverstion

Question

Hi My sql has an issue with execution plan warning SQL conversion when I use cast(VALUE1 as varchar(30)) or CONVERT(char,VALUE1). Both way I am getting the warning

table column is numaric (21,4)

any one can help would be highly appreciated .

many thanks

Answer 1

So you have done some conversion from some numeric datatype to Varchar(30). The warning is for that. In most cases I have seen this message benign and can be ignored. It is more of informative message. I cant read much though you have hidden lot of things.

Answer 2

Have you used the conversion in the WHERE clause or JOIN condition? That prevents the usage of an existing index and that causes performance issues; that's why you get a warning.

Answer 3

Hi Ola Thank you for the responce. yes there is where clause and join . Thouse use to join/where clause with dffirent column .
cmVALUE- is numaric
cmVal1 - is character

select T1.NO no, DESC name,
case
when convert(varchar(max),cmVALUE) = '' then convert(varchar(max),cmVALUE)
when cmVALUE= 0 then convert(varchar(max),ATVALUE)
else convert(varchar(max),cmVALUE)
end cmVal1
from echema.tab1
where class = 'XV'
and PNO is not null