储存过程怎么让一条带有变量的SQL语句在变量前后加单引号

ALTER PROCEDURE [dbo].[proc_business]
　@user varchar(20),
　@city varchar(20),
AS

BEGIN
　declare @wheretrue varchar(100)
　if(@city='') set @wheretrue='select DEPT_CODE from T_USERDEPT where USER_NO='+@user+''
　else set @wheretrue ='select DEPT_CODE from T_DEPT where BRANCH_CODE='+@city+''

　select * from P_BUSINESS_LIST where DEPT_CODE in (@wheretrue)
END

我是想根据@city这个参数有没有值来产生不同的条件，条件是产生了
select DEPT_CODE from T_DEPT where BRANCH_CODE=HGZL002
可是BRANCH_CODE，USER_NO这两个字段是varchar类型的，所以产生出来的SQL因为少了两个单引号怎么也查不到值。

SQL code

set @wheretrue ='select DEPT_CODE from T_DEPT where BRANCH_CODE='''+@city+''''

SQL code

if(@city='') set @wheretrue='select DEPT_CODE from T_USERDEPT where USER_NO='''+@user+''''
　else set @wheretrue ='select DEPT_CODE from T_DEPT where BRANCH_CODE='''+@city+''''

'''来转义。

SQL code

ALTER PROCEDURE [dbo].[proc_business]
　@user varchar(20),
　@city varchar(20),
AS

BEGIN
　declare @wheretrue varchar(100)
　if(@city='') set @wheretrue='select DEPT_CODE from T_USERDEPT where USER_NO='''+ltrim(@user)+''''
　else set @wheretrue ='select DEPT_CODE from T_DEPT where BRANCH_CODE='''+@city+''''

　select * from P_BUSINESS_LIST where DEPT_CODE in (' +ltrim(@wheretrue)+ ')
END

SQL code

ALTER PROCEDURE [dbo].[proc_business]
　@user varchar(20),
　@city varchar(20),
AS

BEGIN
　declare @wheretrue varchar(100)
　if(@city='') set @wheretrue='select DEPT_CODE from T_USERDEPT where USER_NO='''+ltrim(@user)+''''
　else set @wheretrue ='select DEPT_CODE from T_DEPT where BRANCH_CODE='''+@city+''''

　exec('select * from P_BUSINESS_LIST where DEPT_CODE in (' +ltrim(@wheretrue)+ ')')
END