SQL Update when not null - sql

Question

I'm trying to set a column in the fabcon table only if the original column is null.
This is the code I've already tried.
UPDATE dbo.fabcon
SET ext = COALESCE(ext, ( SELECT CASE WHEN [<3] IS NOT NULL THEN '3' END AS extent
FROM dbo.spreadsheetData ))
This is the error I'm getting:
Sub-query returned more than 1 value. This is not permitted when the sub-query follows =, !=, <, <= , >, >= or when the sub-query is used as an expression.
Can anyone see where I've gone wrong?
Thanks. :)
EDIT: the two tables fabcon and spreadsheetData are linked by a column called main1
EDIT2: I've updated the query to this:
UPDATE dbo.fabcon
SET ext = (SELECT CASE WHEN [<3] IS NOT NULL THEN '3' END
FROM dbo.spreadsheetData ssd
WHERE ssd.id = fabcon.id
)
WHERE ext IS NULL;
However, its still failing with the same error.

Answer 1

You need a link between the table fabcon and spreadsheetData. Assuming it is called id:
UPDATE dbo.fabcon
SET ext = (SELECT CASE WHEN [<3] IS NOT NULL THEN '3' END)
FROM dbo.spreadsheetData ssd
WHERE ssd.id = fabcon.id
)
WHERE ext IS NULL;
Note that I removed the coalesce() and replaced it with a where clause for the update. This prevents the query from updating rows unnecessarily (with unchanged values).

Answer 2

DECLARE #PAth INT
Select #path = COALESCE(ext,'')+[<3]+';' FROM dbo.spreadsheetData
UPDATE dbo.fabcon
SET ext = CASE WHEN #PAth IS NOT NULL
THEN '3' ELSE ''
END AS Extent
FROM dbo.fabcon f WHERE f.id = #path
may be this works i think

Answer 3

This should work for you. Assuming I have understood your original query correctly
UPDATE dbo.fabcon
SET
ext = ssd.[column to insert data from]
FROM
dbo.spreadsheetData ssd
WHERE
ext IS NULL
AND
fabcon.id = ssd.id
This assumes the id in the ssd table is the id from the fabcon table. Otherwise just change the id matching based on your column specification

Answer 4

UPDATE dbo.fabcon
SET ext = (SELECT TOP 1 CASE WHEN [<3] IS NOT NULL THEN '3' END
FROM dbo.spreadsheetData ssd
WHERE ssd.main1 = fabcon.main1
ORDER BY 1
)
WHERE ext IS NULL;
with the 2 tables related via "main1" (as now indicated) and an arbitrary "TOP 1" thrown in to avoid the error, this might work.
but: the best way to get an answer is to provide some sample data and an expected result