How to get the full row of data based on max value? - sql

Question

I have an Oracle table with a usage counter. I need to get the full row of data for each sensor with the max counter value?
For ALO I need data in row 2.
For AMA I need data in row 10.
For A11 I need data in row 9658.
For MSP I need data in row 9659.
Any help would be greatly appreciated!
Thanks,
Dave

Answer 1

You can use window function.
selcet * from (
select a.*, row_number() over (partition by facility_id_n
order by usage_counter_n desc) rn
from your_tbl a)
where rn =1;
Or use the First window-funcrion.

Answer 2

ROW_NUMBER won't return correct result if there are two rows with the same USAGE_COUNTER_N value per FACILITY_ID_N. For example:
SQL> WITH test
2 AS (SELECT 9640 ID_n, 'ALO' sensor_id_c, 317 usage_counter_n FROM DUAL
3 UNION
4 SELECT 9641, 'ALO', 18 FROM DUAL
5 UNION
6 SELECT 9642, 'ALO', 0 FROM DUAL
7 UNION
8 SELECT 9659, 'MSP', 25 FROM DUAL --> MAX for MSP ...
9 UNION
10 SELECT 9660, 'MSP', 10 FROM DUAL
11 UNION
12 SELECT 1000, 'MSP', 25 FROM DUAL --> ... but this is also MAX for MSP
13 )
14 SELECT *
15 FROM (SELECT a.*,
16 ROW_NUMBER ()
17 OVER (PARTITION BY sensor_id_c
18 ORDER BY usage_counter_n DESC) rn
19 FROM test a)
20 WHERE rn = 1;
ID_N SEN USAGE_COUNTER_N RN
---------- --- --------------- ----------
9640 ALO 317 1
1000 MSP 25 1
SQL>
RANK might be better:
SQL> l16
16* ROW_NUMBER ()
SQL> c/row_number/rank
16* rank ()
SQL> /
ID_N SEN USAGE_COUNTER_N RN
---------- --- --------------- ----------
9640 ALO 317 1
1000 MSP 25 1
9659 MSP 25 1
SQL>
Or, using the oldfashioned way:
14 SELECT *
15 FROM test t
16 WHERE t.usage_counter_n = (SELECT MAX (t1.usage_counter_n)
17 FROM test t1
18 WHERE t1.sensor_id_c = t.sensor_id_c)
19 ORDER BY sensor_id_c;
ID_N SEN USAGE_COUNTER_N
---------- --- ---------------
9640 ALO 317
9659 MSP 25
1000 MSP 25
SQL>

Answer 3

Depending on your requirements to handle duplicates, the KEEP clause might also be a useful option
SQL> with test
2 AS (SELECT 9640 ID_n, 'ALO' sensor_id_c, 317 usage_counter_n FROM DUAL
3 UNION
4 SELECT 9641, 'ALO', 18 FROM DUAL
5 UNION
6 SELECT 9642, 'ALO', 0 FROM DUAL
7 UNION
8 SELECT 9659, 'MSP', 25 FROM DUAL --> MAX for MSP ...
9 UNION
10 SELECT 9660, 'MSP', 10 FROM DUAL
11 UNION
12 SELECT 1000, 'MSP', 25 FROM DUAL --> ... but this is also MAX for MSP
13 )
14 SELECT sensor_id_c,
15 min(id_n) keep ( dense_rank first order by usage_counter_n DESC ) id_n,
16 min(usage_counter_n) keep ( dense_rank first order by usage_counter_n DESC ) usage_counter_n
17 from test
18 group by sensor_id_c;
SEN ID_N USAGE_COUNTER_N
--- ---------- ---------------
ALO 9640 317
MSP 1000 25