Переписать запрос

SELECT *
 FROM tab_A
 LEFT JOIN tab_B ON tab_A.col_1 = tab_B.CODE
 LEFT JOIN tab_C ON 
	 CASE WHEN ISNULL(tab_A.col_1,"") <> "" and ISNULL(tab_B.col_2,"" ) <> "" 
	    THEN tab_B.col_2 = tab_C.col_3
		ELSE tab_A.col_4 = tab_C.col_3
	 END
	 AND	 tab_C.col_5 = 'Val_1'
 WHERE
		(tab_A.col_6 <> "" OR tab_A.col_6 IS NOT NULL)