T-SQL multiple WHERE clause if the string is empty - sql-server

Question

I have three fields I want to filter my query by. I want to query even if 1 or 2 of the fields are empty (passing an empty string). I can figure out 1 field, but once I add the other two, I do not get any results. Curly brackets are my form fields that get passed to the query.
IF '{Envelope Size}' <> ''
SELECT Tools.ToolNo,
Tools.[Name]
FROM Tools
LEFT JOIN
(
SELECT AdditionalInfo.OwnerID,
AdditionalInfo.UserDefined3,
AdditionalInfo.UserDefined4,
AdditionalInfo.UserDefined5,
AdditionalInfo.UserDefined10,
AdditionalInfo.UserDefined24
FROM AdditionalInfo
WHERE AdditionalInfo.ModuleID = 35
) AS EnvStyle ON Tools.ToolID = EnvStyle.OwnerID
WHERE EnvStyle.UserDefined24 LIKE '{Envelope Size}';
ELSE
SELECT Tools.ToolNo,
Tools.[Name]
FROM Tools
LEFT JOIN
(
SELECT AdditionalInfo.OwnerID,
AdditionalInfo.UserDefined3,
AdditionalInfo.UserDefined4,
AdditionalInfo.UserDefined5,
AdditionalInfo.UserDefined12
FROM AdditionalInfo
WHERE AdditionalInfo.ModuleID = 35
) AS EnvStyle ON Tools.ToolID = EnvStyle.OwnerID
WHERE EnvStyle.UserDefined3 <> 'Stationery'
AND EnvStyle.UserDefined4 = (CASE WHEN '{Env. Height}' = '' THEN 'NULL' ELSE '{Env. Height}' END)
AND EnvStyle.UserDefined5 = (CASE WHEN '{Env. Width}' = '' THEN 'NULL' ELSE '{Env. Width}' END)
AND EnvStyle.UserDefined12 = (CASE WHEN '{Flap Size}' = '' THEN 'NULL' ELSE '{Flap Size}' END);

Answer 1

I'm not exactly clear on what your data structure is and the curly braces are throwing me off a bit, but maybe something like this might work for you. You could change your filter conditions to use an OR with a CASE to force a match in those cases when the values are blank. Again, I'm not sure of your structure and the below is just following your example, but hopefully this might get you in the right direction.
IF '{Envelope Size}' <> ''
SELECT Tools.ToolNo,
Tools.[Name]
FROM Tools
LEFT JOIN
(
SELECT AdditionalInfo.OwnerID,
AdditionalInfo.UserDefined3,
AdditionalInfo.UserDefined4,
AdditionalInfo.UserDefined5,
AdditionalInfo.UserDefined10,
AdditionalInfo.UserDefined24
FROM AdditionalInfo
WHERE AdditionalInfo.ModuleID = 35
) AS EnvStyle ON Tools.ToolID = EnvStyle.OwnerID
WHERE EnvStyle.UserDefined24 LIKE '{Envelope Size}';
ELSE
SELECT Tools.ToolNo,
Tools.[Name]
FROM Tools
LEFT JOIN
(
SELECT AdditionalInfo.OwnerID,
AdditionalInfo.UserDefined3,
AdditionalInfo.UserDefined4,
AdditionalInfo.UserDefined5,
AdditionalInfo.UserDefined12
FROM AdditionalInfo
WHERE AdditionalInfo.ModuleID = 35
) AS EnvStyle ON Tools.ToolID = EnvStyle.OwnerID
WHERE EnvStyle.UserDefined3 <> 'Stationery'
AND (EnvStyle.UserDefined4 = {Env.Height}
OR 1 = CASE WHEN {Env.Height} = '' THEN 1 ELSE 0 END)
AND (EnvStyle.UserDefined5 = {Env.Width}
OR 1 = CASE WHEN {Env.Width} = '' THEN 1 ELSE 0 END)
AND (EnvStyle.UserDefined12 = {Flap Size}
OR 1 = CASE WHEN {Flap Size} = '' THEN 1 ELSE 0 END);