How to convert VARCHAR2 to INTERVAL - sql

Question

I want to convert a VARCHAR2-value like '-28:15:00' to INTERVAL.
With a literal value, this works:
select interval '-09:11:36' hour to second from dual;
However, this does not (ORA-00923: FROM keyword not found where expected):
select interval MY_VARCHAR hour to second from MY_TABLE;
--comparable to select interval to_char(sysdate, 'hh:mm:ss') hour to second from dual;
My assumption is that the literal value is implicitly cast while the explicit varchar-value from MY_VARCHAR (or char from to_char respectively) is not valid between "interval" and "hour".
CAST like this does not work (ORA-00963: unsupported interval type):
select cast(MY_VARCHAR as interval hour to second) from MY_TABLE;
--comparable to select cast('09:11:36' as interval hour to second) from dual;
What does work is concatenating '0 ' as the day-value and cast it to INTERVAL DAY TO SECOND:
select cast('0 ' || '09:11:36' as interval day to second) from dual;
However this only works for positive values, and as long as the value for hour is below 24.
Is there a better solution than dissecting the VARCHAR-value with CASE, SUBSTR and so on?

Answer 1

You need the minus sign before the days to cast it to an interval:
SELECT value,
CAST( REGEXP_REPLACE(value, '^(-)?', '\10 ') AS INTERVAL DAY TO SECOND )
AS interval_value
FROM table_name
or, using simple string functions, which slightly more to type but probably more efficient (as regular expressions are slow):
SELECT value,
CAST(
CASE
WHEN value LIKE '-%'
THEN '-0 ' || SUBSTR(value, 2)
ELSE '0 ' || value
END
AS INTERVAL DAY TO SECOND
) AS interval_value
FROM table_name
Which, for the sample data:
CREATE TABLE table_name (value) AS
SELECT '-09:11:36' FROM DUAL UNION ALL
SELECT '09:11:36' FROM DUAL;
Both output:
VALUE
INTERVAL_VALUE
-09:11:36
-00 09:11:36.000000
09:11:36
+00 09:11:36.000000
fiddle

Answer 2

Another approach, which would accept hour values greater than 23, is to coerce the string into ISO format and use the to_dsinterval() function:
select my_varchar,
to_dsinterval(
regexp_replace(my_varchar, '(-?)(\d+):(\d+):(\d+)', '\1PT\2H\3M\4S')
) as interval_value
from my_table
MY_VARCHAR
INTERVAL_VALUE
-09:11:36
-000000000 09:11:36.000000000
09:11:36
+000000000 09:11:36.000000000
28:15:02
+000000001 04:15:02.000000000
-28:15:02
-000000001 04:15:02.000000000
fiddle
You could do reformatting of the string with string functions, which as #MTO mentioned will be faster for large amounts of data, but it would be a bit messy:
select my_varchar,
to_dsinterval(
case
when substr(my_varchar, 1, 1) = '-'
then '-PT' || substr(my_varchar, 2, instr(my_varchar, ':', 1, 1) - 2)
else 'PT' || substr(my_varchar, 1, instr(my_varchar, ':', 1, 1) - 1)
end || 'H'
|| substr(my_varchar, instr(my_varchar, ':', 1, 1) + 1,
instr(my_varchar, ':', 1, 2) - instr(my_varchar, ':', 1, 1) - 1) || 'M'
|| substr(my_varchar, instr(my_varchar, ':', 1, 2) + 1) || 'S'
) as interval_value
from my_table
MY_VARCHAR
INTERVAL_VALUE
-09:11:36
-000000000 09:11:36.000000000
09:11:36
+000000000 09:11:36.000000000
28:15:02
+000000001 04:15:02.000000000
-28:15:02
-000000001 04:15:02.000000000
fiddle
As shown in the documentation, interval literals (like all literals, as the name implies) require a fixed value, not an expression or column; the quotes are not optional in the railroad diagram:
... so your first query gets ORA-00923.
And the cast() function only supports certain conversions:
Note 1: Datetime/interval includes DATE, TIMESTAMP, TIMESTAMP WITH TIMEZONE, TIMESTAMP WITH LOCAL TIME ZONE, INTERVAL DAY TO SECOND, and INTERVAL YEAR TO MONTH.
so you can't cast(... as interval hour to second), and that will throw ORA-00963.