1. Group Operations
Part IV

2. Aggregate Functions
Summarizes the results of a query over a number of rows, returning a single value.
aggregate_function([DISTINCT | ALL] expression)
aggregate_function: The name of the function
DISTINCT: Consider only unique values from expression
ALL: Consider all values, including duplicates, from expression
expression: Specifies a column or other query on which to perform the aggregation

3. Aggregate Functions SUM COUNT AVG MAX MIN
Returns the total of a numeric column or expression
COUNT
Returns the number of rows matching the criteria of the expression
AVG
Returns the average of a numeric column or expression
MAX
Returns the largest value from a column or expression
MIN
Returns the smallest value from a column or expression

4. Effect of NULL Values
Aggregate functions, except COUNT(*), ignore NULLs – COUNT(*) counts rows, not values
SELECT COUNT(*) addresses 3,213,097
,COUNT(spraddr_to_date) to_dates 1,479,767
FROM spraddr
SELECT AVG(ssbsect_bill_hrs)
FROM ssbsect
WHERE ssbsect_subj_code = 'ACT'
AND ssbsect_term_code = '201990'
SELECT AVG(NVL(ssbsect_bill_hrs, 0))

5. Group By
Combines a result set into multiple groups and produces a single row of summary data for each group.
SELECT c.scbcrse_coll_code college
,COUNT(*) courses
FROM scbcrse c
WHERE c.scbcrse_eff_term =
(SELECT MAX(cx.scbcrse_eff_term)
FROM scbcrse cx
WHERE cx.scbcrse_subj_code = c.scbcrse_subj_code
AND cx.scbcrse_crse_numb = c.scbcrse_crse_numb
AND csus_f_cur_term() >= cx.scbcrse_eff_term)
AND c.scbcrse_csta_code = 'A'
GROUP BY c.scbcrse_coll_code
ORDER BY college

6. Group By
Results

7. Group By
Columns or expressions contained in the SELECT clause that includes an aggregate function must also be included in the GROUP BY clause.
SELECT c.scbcrse_coll_code college
,COUNT(*) courses
FROM scbcrse c
ORDER BY college

8. Having The HAVING clause defines a filter for the GROUP BY clause.
WHERE : SELECT as HAVING : GROUP BY
SELECT c.scbcrse_coll_code college
,c.scbcrse_credit_hr_low low_credits
,COUNT(*) courses
FROM scbcrse c
WHERE c.scbcrse_eff_term =
(SELECT MAX(cx.scbcrse_eff_term)
FROM scbcrse cx
WHERE cx.scbcrse_subj_code = c.scbcrse_subj_code
AND cx.scbcrse_crse_numb = c.scbcrse_crse_numb
AND csus_f_cur_term() >= cx.scbcrse_eff_term)
AND c.scbcrse_csta_code = 'A'
GROUP BY c.scbcrse_coll_code
,c.scbcrse_credit_hr_low
HAVING c.scbcrse_credit_hr_low > 5
ORDER BY college

9. HAVING
Results w/o HAVING
Results w/ HAVING

10. Having
The HAVING clause may only refer to expressions in the SELECT list, or to an expression involving an aggregate function
SELECT c.scbcrse_coll_code college
,COUNT(*) courses
FROM scbcrse c
WHERE c.scbcrse_eff_term =
(SELECT MAX(cx.scbcrse_eff_term)
FROM scbcrse cx
WHERE cx.scbcrse_subj_code = c.scbcrse_subj_code
AND cx.scbcrse_crse_numb = c.scbcrse_crse_numb
AND csus_f_cur_term() >= cx.scbcrse_eff_term)
AND c.scbcrse_csta_code = 'A'
GROUP BY c.scbcrse_coll_code
HAVING COUNT(*) > 700
ORDER BY college

11. Having
Results w/o HAVING
Results w/ HAVING

12. Questions?