i want to show the faculty rating from the database using sql server

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C#

My query as follows;

 SELECT F.facname, 
       BA.examdate, 
       FD.bfid, 
       FD.rate 
FROM   faculty F 
       JOIN bthfac B 
         ON F.facid = B.facid 
       JOIN facfeedback FD 
         ON FD.bfid = B.bfid 
       JOIN batch BA 
         ON BA.bthid = B.bthid 	

when i execute the above query, shows error as follows;

Error converting data type varchar to bigint.


faculty table database structure as follows;

FacId         bigint
FacName   varchar
Fac_active    char(1)

bthfac table database structure as follows;

BFid     bigint
BthId    bigint
FacId    varchar(40)

facfeedback table database structure as follows;

BFid  bigint
Rate   int

Batch table database structure as follows;

 BthId	    bigint	
Examdate   datetime

what is the problem in my above query.

please help me.

regards,
narasiman P.