c# - Linq to SQL Query Slow -

i'm trying following sql query linq sql.

select  course_sections.sec_subject,         course_sections.sec_course_no,         course_sections.sec_no,         sectionenrollments.sectionenrollment    course_sections         inner join  (select stc_course_name, stc_section_no, count(*) sectionenrollment                student_acad_cred               stc_term = '2012fl'         group       stc_course_name, stc_section_no) sectionenrollments                     on course_sections.sec_subject + '-' + course_sections.sec_course_no = sectionenrollments.stc_course_name                        , course_sections.sec_no = sectionenrollments.stc_section_no   sec_term = '2012fl' 

my first attempt this

var query = sections in db.course_sections     sections.sec_term == "2012fl"     orderby sections.sec_subject, sections.sec_course_no, sections.sec_no     select          new          {              sections.sec_subject,              sections.sec_course_no,              sections.sec_no,             sectionenrollmentcount = (from enrollments in db.student_acad_cred                 enrollments.stc_term == "2012fl"                 group enrollments                     new                     {                         stc_course_name = enrollments.stc_course_name,                         stc_section_no = enrollments.stc_section_no                     } grouping                 grouping.key.stc_course_name == sections.sec_subject + "-" + sections.sec_course_no                     && grouping.key.stc_section_no == sections.sec_no                 select grouping.count()).firstordefault()         }; 

this actual works takes 30 return results (about 900 records). sql takes under second.

this next attempt try run faster.

var query2 = sections in db.course_sections     join groupingquery in          (from enrollments in db.student_acad_cred         enrollments.stc_term == "2012fl"         group enrollments             new             {                 stc_course_name = enrollments.stc_course_name,                 stc_section_no = enrollments.stc_section_no             } grouping         select new { grouping.key, enrollmentcount = grouping.count() } )         on sections.sec_subject + "-" + sections.sec_course_no + "-" + sections.sec_no equals groupingquery.key.stc_course_name + "-" + groupingquery.key.stc_section_no         sectionenrollmentcount     sections.sec_term == "2012fl"     orderby sections.sec_subject, sections.sec_course_no, sections.sec_no     select         new         {             sections.sec_subject,             sections.sec_course_no,             sections.sec_no,         sectionenrollmentcount         }; 

however, sectionenrollmentcount variable type system.collections.generic.list1[<>f__anonymoustype22[<>f__anonymoustype0`2[system.string,system.string],system.int32]] , can't figure out how become number.

can me work?

thanks,

edit

this sql first attempt generating.

select  [project1].[c1] [c1],  [project1].[sec_subject] [sec_subject],  [project1].[sec_course_no] [sec_course_no],  [project1].[sec_no] [sec_no],  [project1].[c2] [c2] ( select  [filter1].[sec_subject] [sec_subject],  [filter1].[sec_course_no] [sec_course_no],  [filter1].[sec_no] [sec_no],  1 [c1],  case when ([limit1].[a1] null) 0 else [limit2].[a1] end [c2]    (select [extent1].[sec_subject] [sec_subject], [extent1].[sec_course_no] [sec_course_no], [extent1].[sec_no] [sec_no]     [dbo].[course_sections] [extent1]     '2012fl' = [extent1].[sec_term] ) [filter1] outer apply  (select top (1) [groupby1].[a1] [a1]     ( select          [extent2].[stc_course_name] [k1],          [extent2].[stc_section_no] [k2],          count(1) [a1]         [dbo].[student_acad_cred] [extent2]         '2012fl' = [extent2].[stc_term]         group [extent2].[stc_course_name], [extent2].[stc_section_no]     )  [groupby1]     ([groupby1].[k1] = ([filter1].[sec_subject] + n'-' + [filter1].[sec_course_no])) , ([groupby1].[k2] = [filter1].[sec_no]) ) [limit1] outer apply  (select top (1) [groupby2].[a1] [a1]     ( select          [extent3].[stc_course_name] [k1],          [extent3].[stc_section_no] [k2],          count(1) [a1]         [dbo].[student_acad_cred] [extent3]         '2012fl' = [extent3].[stc_term]         group [extent3].[stc_course_name], [extent3].[stc_section_no]     )  [groupby2]     ([groupby2].[k1] = ([filter1].[sec_subject] + n'-' + [filter1].[sec_course_no])) , ([groupby2].[k2] = [filter1].[sec_no]) ) [limit2] )  [project1] order [project1].[sec_subject] asc, [project1].[sec_course_no] asc, [project1].[sec_no] asc 

this linq-to-sql command works

from section in db.course_sections join sectionenrollments in (     (from  student_acad_cred in db.student_acad_cred         student_acad_cred.stc_term == "2012fl"         group student_acad_cred new {             student_acad_cred.stc_course_name,             student_acad_cred.stc_section_no } g         select new {         g.key.stc_course_name,         g.key.stc_section_no,         sectionenrollment = (int64?)g.count()     }))         on section.sec_subject + "-" + section.sec_course_no + "-" + section.sec_no             equals sectionenrollments.stc_course_name + "-" + sectionenrollments.stc_section_no     section.sec_term == "2012fl" orderby section.sec_subject,     section.sec_course_no,     section.sec_no select new {     section.sec_subject,     section.sec_course_no,     section.sec_no,     sectionenrollments.sectionenrollment };