doubt on stored procedure

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SQL

table in db as below,

CREATE TABLE [dbo].[STS_ADDRESS_BOOK](
[AB_ID] int NOT NULL IDENTITY(1,1) CONSTRAINT primarykey PRIMARY KEY,
[AB_NAME] [varchar](100),
[AB_EMAIL] [varchar](100),
[AB_FAX] [varchar](100),
[AB_ADDRESS][varchar](max),
[AB_PHONE][varchar](16)
)
-----------------------------------------------------
then sp,
--------------------------------------------------------
GO
IF OBJECT_ID ('dbo.selectAddressBookInformation1')IS NOT NULL
DROP PROC selectAddressBookInformation1
GO

CREATE PROC selectAddressBookInformation1 @columnvalue varchar(100),
@searchword varchar(100)
AS

exec ('select* from STS_ADDRESS_BOOK where' +@columnvalue+' LIKE %' + @searchword + '%')

this command executed successfully. but when execute sp using,
---------------------------------------------------------------------------
exec selectAddressBookInformation1 @columnvalue=[AB_NAME],@searchword='b'

get error as
--------------------------------------
Incorrect syntax near the keyword 'LIKE'. why? what is the mistake?