DECLARE  @SCHOOLGRADECODE VARCHAR(5)
DECLARE @PROVINCECODE   VARCHAR(5)
DECLARE @SUBJECTCODE   VARCHAR(10)

set @SCHOOLGRADECODE = 'SG01'
set @PROVINCECODE =  'PV01'
set @SUBJECTCODE='SJ010103'

SELECT  provincecode, schoolgradecode, subjectcode, bccode, barcode, bookId, contsId
FROM   tbCSY05 AS TC
WHERE  (schoolgradecode = @SCHOOLGRADECODE OR @SCHOOLGRADECODE = '')
 AND  (provincecode = @PROVINCECODE OR @PROVINCECODE = '')
 AND  (subjectcode = @SUBJECTCODE OR @SUBJECTCODE = '')
GROUP BY provincecode, schoolgradecode, subjectcode, bccode, barcode, bookId, contsId 

위 큰 글씨 부분의 의미가 궁금합니다...