help understanding syntax with proc sql

[marleeakerson]

hello, 

i am having trouble understanding the syntax in this proc sql step. 

My questions are 

1) I am not sure how to figure out where the a vs. b vs. c datasets are coming from. A lot of the variables listed under the select step are not in the OLDTABLE dataset, so i dont know where to look for them. 

2) this step keeps ending early in the log due to an error and i am not sure why: a.RECIP_ID=b.RECIP_ID

thank you! 

proc sql; 
	create table NEWTABLE as
	select b.var1 
	     , 2016 as year  
	     , c.var2 
	     , c.var3 
             , c.var4  
	     , c.var5 
	     , '-' as  var6 
	     , c.var7 
             , a.var8 
	     , a.var9 
	     , a.var10  
	from 
		(select distinct orid
	           , Name as facility
	           , cnty as county
	           , ercategory           
	           , count(*) as visits
	      from OLDTABLE
	      group by 1, 2, 3, 4
	     ) as a 
		 left join
		 (select distinct orid, 
			case  
			when count(*) eq 1 then '1 Visit' 
			when count(*) eq 2 then '2 Visits' 
			when count(*) >2 and count(*)<6  then '3 to 5 Visits' 
			when count(*) >5 and count(*)<11  then '6 to 10 Visits' 
			when count(*) >10 and count(*)<26  then '11 to 25 Visits' 
			when count(*) >25  then '26 + Visits' 
			else
			'No Visits'
			end as ed_freq_cat
			from OLDTABLE
			group by 1
		  ) as b  on a.RECIP_ID=b.RECIP_ID
	      left join 
		  (select * from sdelig.Member_month_rolloff
	where MBR_MTH_YR_MTH between '201607' and '201706') as c
		  on a.RECIP_ID=c.RECIP_ID;
 quit;

[PGStats]

Post the log please.