Create a datetime value from separate date time columns - sql

Question

I have individual columns for year, month, day, hour, minute, second and millisecond. I need to combine them all together into a date timestamp. I am able to make a date value, but can't seem to make a valid time one. I am working in Oracle and I have sample below. I'd like my value to look like the createtime column.
This did the trick:
to_timestamp(XT.MONTH1||'-'||XT.DAY1||'-'||XT.YEAR||' '|| xt.hour24||'.'||xt.minute||'.'||xt.second||'.'||xt.milliseconds,'MM-DD-YYYY HH24:MI:SS.FF')

Answer 1

That is quite easy but not pretty. You convert the columns from datatype NUMBER to VARCHAR2 padded with leading zeros, using fm to suppress any spaces for + or -:
SELECT TO_CHAR(month,'fm00') FROM mytable;
05
Next, you glue the converted columns together with the || operator to get a single, long, string:
SELECT TO_CHAR(year,'fm0000')||TO_CHAR(month,'fm00')|| ...
20200519...
This long string can now be converted to datatype DATE, or, in your case TIMESTAMP as you have milliseconds. You need to specify the date format you used, f.i. 'YYYYMMDD...'
SELECT TO_TIMESTAMP(TO_CHAR(year,'fm0000')|| ... , 'YYYYMM')
A complete example looks like:
SELECT TO_TIMESTAMP(
TO_CHAR(year,'fm0000')||TO_CHAR(month,'fm00')||
TO_CHAR(day,'fm00')||TO_CHAR(hour24,'fm00')||
TO_CHAR(minute,'fm00')||TO_CHAR(second,'fm00')||
TO_CHAR(ms,'fm000')
, 'YYYYMMDDHH24MISSFF3')
FROM (-- your table, as a mockup, I'll use DUAL
SELECT 2020 as year, 5 as month, 19 as day,
13 as hour24, 7 as minute, 10 as second,
300 as ms
FROM DUAL);
2020-05-19 13:07:10,300000000
EDIT:
The fill mode modifier fm supresses a leading space for positive numbers (to make room for the - sign for negative numbers). All parts of a date are positive, so you get a lot of spaces in your string.
SELECT TO_CHAR(x,'99'), TO_CHAR(x,'fm99')
FROM (SELECT -10 as x FROM DUAL UNION ALL SELECT 10 FROM DUAL);
| 10|10|
|-10|-10|
The documentation is a bit hidden under Format Model Modifiers.
Come to think of it, you might as well keep the spaces and adjust your format model:
SELECT TO_TIMESTAMP(
TO_CHAR(year,'0000')||TO_CHAR(month,'00')||
TO_CHAR(day,'00')||TO_CHAR(hour24,'00')||
TO_CHAR(minute,'00')||TO_CHAR(second,'00')||
TO_CHAR(ms,'000')
,' YYYY MM DD HH24 MI SS FF3')
FROm (SELECT 2020 as year, 5 as month, 19 as day,
13 as hour24, 7 as minute, 10 as second,
300 as ms FROM DUAL);