1. SubQueries
Part III

2. Subquery
A subquery is a select statement (inner query) nested within another select statement (outer query)
A subquery is always enclosed within parentheses
Non-Correlated Subquery
Allows each row of an outer query to be compared to the results of the inner query
Correlated Subquery
A subquery that references 1 or more columns from the outer query
Executes every time a row is selected by the outer query

3. Non-Correlated Subquery
SELECT ti.csu_id ,ti.name ,ti.term_gpa FROM csus_term_info_eot_cur ti WHERE ti.term_gpa > (SELECT AVG(tx.term_gpa) FROM csus_term_info_eot_cur tx) ORDER BY ti.term_gpa DESC

4. Correlated Subquery SELECT c.id CSU_ID ,c.name Name
,c.course_reference_number CRN
FROM csus_section_info_cur c
JOIN csus_student_attribute a
ON a.person_uid = c.person_uid
AND a.academic_period = c.academic_period
WHERE a.student_attribute = 'ASHS'
AND NOT EXISTS (SELECT ‘X'
FROM schedule_attribute s
WHERE s.course_reference_number = c.course_reference_number
AND s.academic_period = c.academic_period
AND s.schedule_attribute IN ('DHAN', 'DHHS', 'DHHY', 'DHRI'))
ORDER BY Name

5. Inline View A subquery defined in the FROM clause
The subquery must be named
SELECT a_column a_col
FROM z_table
JOIN (SELECT b_column b_col
FROM y_table) inline_view
ON inline_view.b_col = a_col
After it has been defined, an inline view is treated as if it were another joined table

6. Example Inline View
SELECT x1.ssbxlst_term_code AS term, MAX(xs1.ssrxlst_crn) AS crn, s.ssbsect_subj_code AS subj, s.ssbsect_crse_numb AS crse, s.ssbsect_seq_numb AS sect, x1.ssbxlst_xlst_group AS xlist, summary.max_enrl AS seat_sum, x1.ssbxlst_max_enrl AS xlist_maxseat, s.ssbsect_camp_code AS campus FROM ssbxlst x1 JOIN ssrxlst xs1 ON xs1.ssrxlst_term_code = x1.ssbxlst_term_code AND xs1.ssrxlst_xlst_group = x1.ssbxlst_xlst_group JOIN ssbsect s ON s.ssbsect_term_code = xs1.ssrxlst_term_code AND s.ssbsect_crn = xs1.ssrxlst_crn LEFT OUTER JOIN (SELECT x.ssbxlst_term_code AS term, x.ssbxlst_xlst_group AS grp, SUM(s.ssbsect_max_enrl) AS max_enrl FROM ssbxlst x ON s.ssbsect_term_code = x.ssbxlst_term_code AND s.ssbsect_crn IN (SELECT xs.ssrxlst_crn FROM ssrxlst xs WHERE xs.ssrxlst_term_code = x.ssbxlst_term_code AND xs.ssrxlst_xlst_group = x.ssbxlst_xlst_group) GROUP BY x.ssbxlst_term_code ,x.ssbxlst_xlst_group) summary ON summary.term = x1.ssbxlst_term_code AND summary.grp = x1.ssbxlst_xlst_group
List of cross listed courses where the cross list max enrollment does not equal the sum of the max enrollment for each section.

7. Example Inline View (cont)
WHERE x1.ssbxlst_term_code >= csus_f_cur_term() AND x1.ssbxlst_max_enrl != summary.max_enrl GROUP BY x1.ssbxlst_term_code ,s.ssbsect_subj_code ,s.ssbsect_crse_numb ,s.ssbsect_seq_numb ,x1.ssbxlst_xlst_group ,summary.max_enrl ,x1.ssbxlst_max_enrl ,s.ssbsect_camp_code ORDER BY term ,xlist ,subj ,crse ,sect

8. Questions?