SQLの複数のフィールドの接続

#           
select bid || ocpc_level_desc || pay_mode_desc AS fem_bid from fem_baidu_adgroup
# concat        
select concat(bid,ocpc_level_desc,pay_mode_desc)AS fem_bid from fem_baidu_adgroup
# concat    /  
select concat(bid,'/',ocpc_level_desc,'/',pay_mode_desc)AS fem_bid from fem_baidu_adgroup
# concat   case when            /  
concat(bid,(case ocpc_level_desc when '' then ''else '/'end),ocpc_level_desc,(case pay_mode_desc when '' then ''else '/'end),pay_mode_desc) AS fem_bid,