Copying only certain values from one row into another table - sql

Question

I am trying to copy data from one table to another table, which works fine, but I only want to copy certain data from one the of the columns.
Insert Into Period (Invoice_No, Period_Date)
Select Invoice_Seq_No, Inv_Comment
From Invoices
Where INV_Comment LIKE '%November 2015';
The Inv_Comment column contains free-form comments and the date in different formats, e.g. "paid on November 2015 or "paid on Aug" or "July 2015". What I am trying to do is to copy only the "November 2015" part of the comment into the new table.
The above code only copies the entire data of the Inv_Comment field and I only want to copy the date. The date part can be in one of three formats: MON YYYY, DD.MM.YYYY or only the month i.e. MON
How can I extract only the date part I am interested in?

Answer 1

For your very simple example query you can use the substr() function, using the length of your fixed value to count back from the end of the string, as that document describes:
If position is negative, then Oracle counts backward from the end of char.
So you can do:
select invoice_seq_no, substr(inv_comment, -length('November 2015'))
from invoices
where inv_comment like '%November 2015';
But it's clear from the comments that you really want to find all dates, in various formats, and not always at the end of the free-form text. One option is to search the text repeatedly for all the possible formats and values, starting with the most specific (e.g. DD.MM.YYYY) and then going down to least specific
(e.g. just MON). You could insert just the sequence numbers into your table start with, and then repeatedly update the rows that do not yet have values set:
insert into period (invoice_no) select invoice_seq_no from invoices;
update period p
set period_date = (
select case when instr(i.inv_comment, '15.09.2015') > 0 then
substr(i.inv_comment, instr(i.inv_comment, '15.09.2015'), length('15.09.2015'))
end
from invoices i
where i.invoice_seq_no = p.invoice_no
)
where period_date is null;
then repeat the update with another date, or a more generic November 2015 pattern, etc. But specifying every possible date isn't going to be feasible, so you could regular expressions. There are probably better patterns for this but as an example:
update period p
set period_date = (
select regexp_substr(i.inv_comment, '[[0-3][0-9][-./][0-1][0-9][-./][12]?[901]?[0-9]{2}')
from invoices i
where i.invoice_seq_no = p.invoice_no
)
where period_date is null;
which matches (or attempts to match) anything looking like DD.MM.YYYY, followed by maybe:
update period p
set period_date = (
select regexp_substr(i.inv_comment,
'(Jan(uary)?|Feb(ruary)?|Mar(ch)?|Apr(il)?|May|Jun(e)?|Jul(y)?|Aug(ust)?|'
|| 'Sep(tember)?|Oct(ober)?|Nov(ember)?|Dec(ember)?)([[:space:]]+[12]?[901]?[0-9]{2})?')
from invoices i
where i.invoice_seq_no = p.invoice_no
)
where period_date is null;
which matches any short or long month name. You may have mixed case though - aug, Aug, AUG - so you might want to use the match parameter to make it case-insensitive. This isn't supposed to be a complete solution though, and you may need further formats. There are some ideas on other questions.
You may really want actual dates, which means breaking down a bit more, and then assuming missing years - perhaps taking the year from another column (order date?) if it isn't available in the comments, though that gets a bit messy around year-end. But you can essentially do the same thing, just passing each extracted value through to_date() with a format mask matching the search expression you're using.
There will always be mistakes, typos, odd formatting etc., so even if this approach identified most patterns, you'll probably end up with some that are left blank, and will need to be set manually by a human looking at the comments; and some that are just wrong. But this is why dates shouldn't be stored as strings at all - having them mixed in with other text is just making things even worse.

Answer 2

Here you're dealing with strings containing disparate date information. Several string operations may be needed.