将 SQL_Variant 列修改为 VARCHAR

Question

I have a table where one of the columns has a sql_variant datatype. I'm trying to modify the column to VarChar(800) but I'm getting an error:

Implicit conversion from data type sql_variant to varchar is not allowed. Use the CONVERT function to run this query

I tried using the Convert statement in the Alter statement but I'm getting an incorrect syntax error. I would really appreciate it if someone can shed some light on how this problem can be resolved. Thank you!

Script:

ALTER TABLE dbo.tmpEmployee
ALTER COLUMN bigVal Varchar(800)

bigVal is the column of sql_variant datatype.

This is the error:

Msg 257, Level 16, State 3, Line 5
Implicit conversion from data type sql_variant to varchar is not allowed. Use the CONVERT function to run this query.

Answer 1

I'm afraid this is not an easy task, if the order of column doesn't matter, just add a new column as varchar(800) and try to insert data from sql_varient to that column, but you have to be careful for different type of data in that column to use right casting format for example for dates and binary values

Answer 2

try this query

UPDATE dbo.tmpEmployee
          SET bigVal = CONVERT(varchar(800),bigVal) 
          FROM tmpEmployee

ALTER TABLE dbo.tmpEmployee
ALTER COLUMN bigVal Varchar(800)