how to solve this warning in select
There's nothing to fix, really.

The message refers to this computed column in the Sales.SalesOrderHeader table:

[SalesOrderNumber]  AS (isnull(N'SO'+CONVERT([nvarchar](23),[SalesOrderID]),N'*** ERROR ***')),


The warning is informational in this case, to be sure you're aware in case it was a problem, as discussed in this Q&amp;A: Type conversion in expression may affect “CardinalityEstimate” - on a computed column?