Case with Like operator - sql

Question

Got stuck at using CASE statement with LIKE operator. In the below stored procedure all the parameters are not mandatory so when User doesn't enter PatientName for searching then the below query doesn't return expected results as the LIKE operator is outside which is obvious. I'm looking for something like this so that when User doesn't enter PatientName it will be
(c.LastName + c.Firstname) = #PatientNAme else
(c.LastName + c.Firstname) like '%' + #PatientNAme + '%'
*
(c.LastName + c.Firstname) (
CASE #PatientName
WHEN '' THEN #PatientName = (c.LastName + c.Firstname)
ELSE like '%' + #PatientName + '%'
END
)
*
CREATE proc [dbo].[SearchParkPrescriptionDetails]
#DispenseID INT,
#ParkPrescriptionReasonId INT,
#PrescriptionParkType VARCHAR(50),
#PatientName VARCHAR(120),
#User VARCHAR(120),
#fromdate DATETIME,
#todate DATETIME,
#DateWiseSearch VARCHAR(3),
#PatientID INT
AS
BEGIN
SELECT
a.ParkPrescriptionId
, a.DispenseID
, a.ParkPrescriptionReasonId
, a.ParkDate
, (c.LastName + ' ' + c.Firstname) AS PatientName
, d.PrescriptionType
, e.ParkPrescriptionReason
, a.Notes
, b.ItemCount AS TotalItems
, g.ExemptionReason
,a.[User]
FROM
ParkPrescriptionDetails a
INNER JOIN
Dis_DispenseMaster b
ON
a.DispenseID=b.DispenseID
INNER JOIN
Patient c
ON
b.PatientId = c.PatientId
INNER JOIN
Lookup_PrescriptionType d
ON
b.PrescriptionTypeId = d.PrescriptionTypeId
INNER JOIN
Lookup_ParkPrescriptionReason e
ON
a.ParkPrescriptionReasonId = e.ParkPrescriptionReasonId
LEFT JOIN
Lookup_ExemptionReason g
ON
b.ExemptionReasonId = g.ExemptionReasonId
WHERE
CONVERT(DATE, a.ParkDate) BETWEEN #fromdate AND #todate
AND a.RecallStatus = 'N'
AND a.DispenseID = ( CASE #DispenseID WHEN 0 THEN a.DispenseID ELSE #DispenseID END )
AND b.PatientId = ( CASE #PatientID WHEN 0 THEN b.PatientId ELSE #PatientID END )
AND a.ParkPrescriptionReasonId = ( CASE #ParkPrescriptionReasonId WHEN 0 THEN a.ParkPrescriptionReasonId ELSE #ParkPrescriptionReasonId END )
AND
(
c.LastName + c.Firstname
) LIKE ( CASE #PatientName WHEN '' THEN (c.LastName + c.Firstname) ELSE '%' + #PatientName + '%' END )
AND a.[User] LIKE ( CASE #User WHEN '' THEN a.[User] ELSE '%' + #User + '%' END )
AND b.ParkPrescription = ( CASE #PrescriptionParkType WHEN '' THEN b.ParkPrescription WHEN 'Park' THEN 'Y' END )
AND b.RecallPrescription = ( CASE #PrescriptionParkType WHEN '' THEN b.RecallPrescription WHEN 'Recall' THEN 'Y' END )
AND a.IsDeleted =0
END
========== Changed it Like this. Is this perfect ===========
(c.LastName + ' ' + c.Firstname) = (
CASE #PatientName
WHEN '' THEN (c.LastName + ' ' + c.Firstname)
ELSE '%' + #PatientName + '%'
END
)

Answer 1

Do not use CASE WHEN in where clause. Use OR
(
#PatientName = '' OR
(c.LastName + c.Firstname) LIKE '%' + #PatientName + '%'
) AND
(
#User = '' OR
a.[User] LIKE '%' + #User + '%'
) -- Same for others
instead of
(c.LastName + ' ' + c.Firstname) = (
CASE #PatientName
WHEN '' THEN (c.LastName + ' ' + c.Firstname)
ELSE '%' + #PatientName + '%'
END
)

Answer 2

T-SQL has two forms of CASE. You are using "Simple Case". Try "Searched Case" - e.g.:
CASE
WHEN #PatientName = '' THEN [ return something ]
WHEN #PatientName like [ pattern ] THEN [ return something ]
ELSE [ return something else ]
END