SQL语句中单引号

declare @SearchType nvarchar(50)
declare @SearchString nvarchar(255)
declare @SearchKey nvarchar(50)
declare @SearchSql nvarchar(2000)

set @SearchType = '2'
set @SearchKey = 'd'

set @SearchString = CASE @SearchType 
                            when '1'  then '1 = 1'
                            when '2'  then  'p.ProjectName like ''' + '%'  +  @searchkey + '%'  + ''''
                            when '3'  then  'p.ProjectCity like ''' + '%'+ @searchkey + '%' +''''
                            when '4'  then  'c.CateName like '''  + '%' + @searchkey + '%' + ''''
                            when '4'  then  'p.ProjectManager like ''' + '%' + @searchkey + '%' +'''' 
                            END

set @SearchSql = N'

SELECT p.*,datename(year,ProjectPostTime)+ '   +  '''-''' + ' + datename(month,ProjectPostTime)+ '+ '''-''' + ' + datename(day,ProjectPostTime)' + ' as PostTime, m.EmpName,c.CateName FROM tableddd As p ,tableeee As m ,tablefff c WHERE p.EmpID = m.EmpID and p.CateID = c.CateID  and '
 
 + @SearchString