Dynamic UPDATE statement - sql

Question

I want to create a dynamic update query where I need to set a certain value in a column. But the column name needs to be SELECTed from another table.
I have already the following query:
UPDATE core.TableRes
SET (
SELECT Code FROM core.TableFields
INNER JOIN core.TableXTableFields ON TableXTableFields.FieldID = TableFields.FieldID
INNER JOIN core.TableResRefLinks ON TableResRefLinks.ExtraFieldID = TableXTableFields.ExtraFieldID
WHERE TableResRefLinks.TableResRefLinksID = RefLinks.TableResRefLinksID)
= (
SELECT Value FROM core.TableResRefLinks WHERE TableResRefLinksID = RefLinks.TableResRefLinksID)
FROM core.TableRes
INNER JOIN core.TableResRefLinks RefLinks ON RefLinks.ResourceID = TableRes.ResourceID
INNER JOIN core.TableXTableFields ON TableXTableFields.ExtraFieldID = RefLinks.ExtraFieldID
INNER JOIN core.TableFields ON TableFields.FieldID = TableXTableFields.FieldID
WHERE (EndDate IS NULL OR EndDate > GETDATE()) AND
(
SELECT Code FROM core.TableFields
INNER JOIN core.TableXTableFields ON TableXTableFields.FieldID = TableFields.FieldID
INNER JOIN core.TableResRefLinks ON TableResRefLinks.ExtraFieldID = TableXTableFields.ExtraFieldID
WHERE TableResRefLinks.TableResRefLinksID = RefLinks.TableResRefLinksID)
<>
(
SELECT Value FROM core.TableResRefLinks
WHERE TableResRefLinksID = RefLinks.TableResRefLinksID)
It gives me the following errors:
Msg 102, Level 15, State 1, Line 2
Incorrect syntax near '('.
Msg 102, Level 15, State 1, Line 3
Incorrect syntax near '='.
Msg 156, Level 15, State 1, Line 5
Incorrect syntax near the keyword 'FROM'.
Msg 102, Level 15, State 1, Line 14
Incorrect syntax near '<'.
Is there a way to solve this? If I change the complete UPDATE and SET statements and replace them with a SELECT *, I get results.
EDIT
Here are the datatypes
TableFields.Code => nvarchar(100)
TableResRefLinks.Value => sql_variant
And the datatypes of the columns that have as column name TableFields.Code are set as sql_variant

Answer 1

You can't solve this using plain SQL. You would need some kind of scripting to build your statement. For example postgresql has a scripting language called "pgpsql" which allows building dynamic SQL statements. But this clearly depends on the underlying RDBMS.
By the way: this works with SELECT as you are doing simple sub-select.