OracleSQL CASE Statement on Number in string - sql

Question

I have a table called TEST_TABLE with 1 column called COLUMN1. This table has 2 records:
V.WEEKLY_2020_15
V.WEEKLY_2020_16
I'm trying to write a CASE statement that maps these records to different Periods. e.g.
SELECT
CASE WHEN COLUMN1='V.WEEK_2020_ **MAXIMUM NUMBER** ' THEN 'CURRENT PERIOD'
ELSE 'HISTORICAL PERIOD 1' END
FROM TEST_TABLE
I'm not sure what is the best way to do this though. I need to get the number from the end of the string, and then compare it to the other numbers in the table. Once it finds one number that is higher or lower it can stop the search as there will always only be 2 numbers in this table.

Answer 1

You can get the number from the end of the string with a regular expression. This one gets the 3rd group of characters which don't include an underscore.
select column1, regexp_substr(column1,'[^_]+',1,3) from test_table;
Alternately you could get the 2nd group of numbers with regexp_substr(column1,'[0-9]+',1,2). The best regexp will depend on your knowledge of the possible string values. If you know the number will always be the last 2 characters, you could do substr(column1, -2)
And if you want to identify rows which have the highest/lowest/etc value, adding a column which applies an window/analytical function is a common pattern.
-- sample data
with test_table as (select 'V.WEEKLY_2020_15' as column1 from dual
union select 'V.WEEKLY_2020_16' from dual)
-- query
SELECT column1, regexp_substr(column1,'[^_]+',1,3) as regex, max_number,
CASE WHEN COLUMN1=max_number THEN 'CURRENT PERIOD'
ELSE 'HISTORICAL PERIOD 1' END as period
FROM (select test_table.*,
max(column1) over (order by regexp_substr(column1,'[^_]+',1,3) desc) as max_number
from test_table) T;
Usually the data will be more complicated then you're showing - for example, you might have 2 periods in the table for each primary key, and then you'll want to partition your window function.
-- sample data
with test_table as (select 1 as pk, 'V.WEEKLY_2020_15' as column1 from dual
union select 1, 'V.WEEKLY_2020_16' from dual
union select 2, 'V.WEEKLY_2021_1' from dual
union select 2, 'V.WEEKLY_2021_200' from dual)
-- query
SELECT pk, column1, regexp_substr(column1,'[^_]+',1,3) as regex,
CASE WHEN COLUMN1=max_number THEN 'CURRENT PERIOD'
ELSE 'HISTORICAL PERIOD 1' END as period
FROM (select test_table.*,
max(column1) over (partition by pk order by regexp_substr(column1,'[^_]+',1,3) desc) as max_number
from test_table) T;
Output:
PK
COLUMN1
REGEX
PERIOD
1
V.WEEKLY_2020_16
16
CURRENT PERIOD
1
V.WEEKLY_2020_15
15
HISTORICAL PERIOD 1
2
V.WEEKLY_2021_200
200
CURRENT PERIOD
2
V.WEEKLY_2021_1
1
HISTORICAL PERIOD 1