Using SELECT subquery in a CASE statement and handling NULLS - sql

Question

I have 2 SQL tables one holding stock information then a style table which details how the stock is used. For some jobs the information is contained with a print file so the value in the stock table would be BIN, if not it would contain a template name which would cause a query to a Styles table which then shows how the stock is used. There a 10 positions that a stock could be applied but the template table wouldn't have records for where a stock couldn't be used (on the back of a simplex job for example).
I have a stored procedure which works to provide the detail based on whether the logic value is BIN or not but for the records in the style table that have no value I get NULL back which I need to suppress but just putting ISNULL around the column name in the subquery isn't having any effect. Am I just missing something as I'd rather not nest in another CASE statement to check if the query would produce NULL
WITH STYLES AS
(
SELECT
#JOBNAME AS JobName, Logic AS StyleName
FROM
[dbo].[CON_Tbl_511_DigitalStocks]
WHERE
JOBNAME = #JOBNAME
)
SELECT TOP 1
[Logic],
[S1F], [S1B], [S2F], [S2B],
[S3F], [S3B], [S4F], [S4B],
[S5F], [S5B],
CASE
WHEN b.stylename = 'BIN'
THEN --checks if there is a style for this job
CASE
WHEN S1F = '' THEN ''
ELSE '1'
END -- if a stock code is specified then return the bin name ("1")
ELSE (SELECT PAGE
FROM [dbo].[CON_Tbl_512_DigitalLogic]
WHERE STYLENAME = B.StyleName
AND STOCKREF = 'S1F')
END AS S1F_LOGIC, -- If a style is used return the style instruction for this bin and side
CASE
WHEN b.stylename = 'BIN' -- repeat this for all bins/sides
THEN
CASE WHEN S1B = '' THEN ''
ELSE '1'
END
ELSE (SELECT PAGE
FROM [dbo].[CON_Tbl_512_DigitalLogic]
WHERE STYLENAME = B.StyleName AND STOCKREF = 'S1B')
END AS S1B_LOGIC,
CASE WHEN b.stylename = 'BIN' THEN
CASE WHEN S2F = '' THEN ''
ELSE '2' END
ELSE (SELECT PAGE FROM [dbo].[CON_Tbl_512_DigitalLogic] WHERE STYLENAME = B.StyleName AND STOCKREF = 'S2F') END AS S2F_LOGIC -- this one returns NULL as there is no instruction required for "2SF"
FROM
[CON_Tbl_511_DigitalStocks] A
JOIN
STYLES B ON A.JOBNAME = B.JOBNAME
WHERE
A.JobName = #JobName
This code works fine until the last one as there is no value in the stockref column that says 'S2F' but putting SELECT ISNULL(PAGE, '') still returns NULL

Answer 1

Because this query is not finding any records:
SELECT PAGE FROM [dbo].[CON_Tbl_512_DigitalLogic] WHERE STYLENAME = B.StyleName AND STOCKREF = 'S2F'
and you want it to return something, you can change it to:
SELECT coalesce(min(PAGE),'') FROM [dbo].[CON_Tbl_512_DigitalLogic] WHERE STYLENAME = B.StyleName AND STOCKREF = 'S2F'
This will return the minimum value (min) of the found records, which will return NULL when noting found. The coalesce will turn this NULL into the empty string: ''
P.S.: see also SQL - Difference between COALESCE and ISNULL?