sp_executesql with ISNUMERIC(@ColumnName) not working with column name passed as parameter

**Question**: Why example 1 does not work while example 2 works: **SQL Table to check for non-numeric values in varchar column**: CREATE TABLE #t(Mycol varchar(15)) INSERT #t VALUES ('123.86'),('4a5.67'),('45.68'),('45r8.78') Query to check the NON-NUMERIC values in the table: SELECT Mycol from #t WHERE ISNUMERIC(Mycol) = 0 **Output**: | Mycol | |---------------------| | 4a5.67 | | 45r8.78 | **GOAL**: Achieve the same by using dynamic SQL **Example 1**: Did not work, why? How can we improve this code without declaring variables outside EXECUTE sp_executesql statement; or is it even possible? EXECUTE sp_executesql N'SELECT @colName as Mycol from #t WHERE ISNUMERIC(@colName) = 0', N'@colName varchar(15)', @colName = N'Mycol'; **Output**: | Mycol | |---------------------| | Mycol | | Mycol | | Mycol | | Mycol | **Example 2**: Works - but required more variable declarations. DECLARE @Qry nvarchar(150), @colName varchar(15) = 'Mycol' SET @Qry = N'SELECT ' + @colName + ' FROM #t WHERE ISNUMERIC(' + @colName + ') = 0' EXECUTE sp_executesql @Qry, N'@colName varchar(15)', @colName = N'Mycol'; Output: | Mycol | |---------------------| | 4a5.67 | | 45r8.78 |