sqlserver 多次左关联同一个表时，效率太低

SQL1
select ss.ssyz,zs1.name,ss.ssez,zs2.name,ss.mzys
from CDR.dbo.INPATIENT_HISSYXH as  his_syxh(nolock)
inner join CDR_DZBL..BAGL_BA_SYJBK as basy (nolock) on basy.his_syxh=his_syxh.INPAT_FORM_NO 
inner join  CDR_DZBL..BAGL_BA_SYSSK as ss (nolock)  on basy.syxh=ss.syxh     
left join CDR_SJZD..HIS_YY_ZGBMK as zs1 (nolock) on ss.ssyz=zs1.id   
left join CDR_SJZD..HIS_YY_ZGBMK as zs2 (nolock) on ss.ssez=zs2.id   
left join CDR_SJZD..HIS_YY_ZGBMK as mzys (nolock) on ss.mzys=mzys.id 

SQL2
select ss.ssyz,zs1.name,ss.ssez,zs2.name,ss.mzys,mzys.name
from CDR.dbo.INPATIENT_HISSYXH as  his_syxh(nolock)
inner join CDR_DZBL..BAGL_BA_SYJBK as basy (nolock) on basy.his_syxh=his_syxh.INPAT_FORM_NO 
inner join  CDR_DZBL..BAGL_BA_SYSSK as ss (nolock)  on basy.syxh=ss.syxh      
left join CDR_SJZD..HIS_YY_ZGBMK as zs1 (nolock) on ss.ssyz=zs1.id    
left join CDR_SJZD..HIS_YY_ZGBMK as zs2 (nolock) on ss.ssez=zs2.id   
left join CDR_SJZD..HIS_YY_ZGBMK as mzys (nolock) on ss.mzys=mzys.id ；

问题描述：
执行SQL1语句时，很快，但是执行SQL2语句时，卡死的感觉，执行的很慢。两个SQL只差一个关联的字段。

索引的问题，吧 name 也放到 mzys 的索引的输出列中