Using UPDATE statement with a SELECT statement converting hexadecimal to text - sql

Question

I have a table called Script_Data that has three columns - ScriptID (primary), RowOrder and ScriptData. each row value for ScripData is hexadecimal. For me to make sense of it, I convert it to text. I CAST() the ScriptData column into VarChar datatype using the following query
SELECT ScriptID, RowOrder, CAST(CAST(ScriptData AS varbinary(MAX)) AS varchar(MAX)) AS Converted_SD
FROM Script_Data
Is it possible to UPDATE values in the ScriptData column when converted? I know that I would typically do something like this if not for converting:
UPDATE Script_Data
SET ScriptData='Sales'
WHERE ScriptData='Marketing';
Is it even possible to do something like this when I have it converted from hex to text? I've tried so many different queries, most of which include subqueries, but all failed.
Converting it changes this
| ScriptID | RowOrder | ScriptData |
------------------------------------
| 5008 | 1 | 0x435669787|
to this (I'm over simplifying the results)
| ScriptID | RowOrder | ScriptData |
------------------------------------
| 5008 | 1 | Sales |
EDIT:
My best attempt seems to have been this query
UPDATE Script_Data
SET ScriptData='Engineering'
(SELECT ScriptID, RowOrder, CONVERT(varchar(max), ScriptData)
FROM Script_Data
WHERE ScriptData = 'Accounting')
But SQL is telling me that Implicit conversion from data type varchar to varbinary(max) is not allowed. Use the CONVERT function to run this query. I've tried to use CONVERT in creative ways to satisfy the error, but have not been successful. The ScriptData column is varbinary datatype with -1 length.

Answer 1

It seems you need to cast the new value to varbinary as part of the update.
UPDATE Script_Data SET
ScriptData = CAST('Engineering' AS VARBINARY(MAX))
WHERE CAST(ScriptData AS VARCHAR(MAX)) = 'Accounting'
I won't ask why you are storing strings as varbinary because I'm sure you realise life would be much easier if you just stored it as a varchar.
Here is the test script I used:
declare #ScriptData table (ScriptData varbinary(max));
insert into #ScriptData (ScriptData)
values (0x435669787), (convert(varbinary(max),'Sales'));
select *, convert(varchar(max),ScriptData,3), CAST(ScriptData AS varchar(MAX)) from #ScriptData;
update #ScriptData set
ScriptData = CAST('Marketing' AS VARBINARY(MAX))
where CAST(ScriptData AS varchar(MAX)) = 'Sales';
select *, convert(varchar(max),ScriptData,3), CAST(ScriptData AS varchar(MAX)) from #ScriptData;

Answer 2

For your SELECT query, the analogous UPDATE is to place conversion in the SET command assigning value to a new or different column, not the same column.
UPDATE is not a DDL (data definition language) but a DML (data manipulation language) command. Hence, it only adjusts data but does not change a columns' defined data type. Consider an ALTER command to create a new VARCHAR(MAX) column then run UPDATE to assign value:
ALTER TABLE Converted_SD ADD ScriptData_Text VARCHAR(MAX);
UPDATE Converted_SD
SET ScriptData_Text = CAST(CAST(ScriptData AS varbinary(MAX)) AS varchar(MAX));
Also, since ALTER is a DDL command, use it very sparingly and never in application code or stored procedure since it can adjust table schema and column definitions.