RE: question about regexp_substr
- From: Jackie Brock <J.Brock@xxxxxxxxxxxxx>
- To: amonte <ax.mount@xxxxxxxxx>
- Date: Tue, 16 Dec 2014 22:53:08 +0000
After the A, the first instance of 0 or more non-numeric characters is 0
characters immediately after the 1, so an empty string. The third instance of
0 or more, including the A and the match immediately after the 1 (0 length), is
B. Does that help?
From: amonte [mailto:ax.mount@xxxxxxxxx]
Sent: Tuesday, December 16, 2014 3:04 PM
To: Jackie Brock
Cc: Oracle-L Group
Subject: Re: question about regexp_substr
Hi Jackie
Not sure what do you mean, I did this:
select regexp_substr('A1B2C3D4E', '[^0-9]*', 1, 1) occur_1,
regexp_substr('A1B2C3D4E', '[^0-9]*', 1, 2) occur_2,
regexp_substr('A1B2C3D4E', '[^0-9]*', 1, 3) occur_3,
regexp_substr('A1B2C3D4E', '[^0-9]*', 1, 4) occur_4,
regexp_substr('A1B2C3D4E', '[^0-9]*', 1, 5) occur_5
from dual;
O O O O O
- - - - -
A B C
select regexp_substr('A1B2C3D4E', '[^0-9]+', 1, 1) occur_1,
regexp_substr('A1B2C3D4E', '[^0-9]+', 1, 2) occur_2,
regexp_substr('A1B2C3D4E', '[^0-9]+', 1, 3) occur_3,
regexp_substr('A1B2C3D4E', '[^0-9]+', 1, 4) occur_4,
regexp_substr('A1B2C3D4E', '[^0-9]+', 1, 5) occur_5
from dual;
O O O O O
- - - - -
A B C D E
And I dont understand very well why * gives A, B and C whereas + gives expected
output.
This is how I read it,
regexp_substr('A1B2C3D4E', '[^0-9]*', 1, 1) says start searching from position
1 for first pattern which is non-numeric and no matter if there is any pattern
occurence so A is printed
regexp_substr('A1B2C3D4E', '[^0-9]*', 1, 1) says start searching from position
1 for second pattern which is non-numeric and no matter if there is any pattern
occurence. If I parse the line A is non-numeric therefore is a candidate but I
am looking for the second occurence so I keep on searching, immediately see
number 1 so the pattern is not matched so keep on searching, we now read B
which is non-numeric, satisfies the pattern so it should be printed but it's
not?
2014-12-16 22:42 GMT+01:00 Jackie Brock
<J.Brock@xxxxxxxxxxxxx<mailto:J.Brock@xxxxxxxxxxxxx>>:
☺ Run it with various values where the three is – get the first occurrence,
then the second, then the third, then the fourth – you’ll easily see what it’s
doing.
From: amonte [mailto:ax.mount@xxxxxxxxx<mailto:ax.mount@xxxxxxxxx>]
Sent: Tuesday, December 16, 2014 2:30 PM
To: Jackie Brock
Cc: Oracle-L Group
Subject: Re: question about regexp_substr
Hello Jackie
I know + means > 1 and * > 0 occurence. But I dont see why they give different
results in my example.
I understand that what query is asking with * is
"find in the string any non-numeric character pattern, no matter if the there
is character or not in the third occurence". I dont see why B satisfies such
condition?
Thanks in advance
Alex
2014-12-16 22:23 GMT+01:00 Jackie Brock
<J.Brock@xxxxxxxxxxxxx<mailto:J.Brock@xxxxxxxxxxxxx>>:
The plus sign indicates that it expects at least 1 digit (1 or more). The *
means 0 or more.
From: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>
[mailto:oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>] On
Behalf Of amonte
Sent: Tuesday, December 16, 2014 2:07 PM
To: Oracle-L Group
Subject: question about regexp_substr
Hi people
I have some difficulty understanding applying an operator to the pattren in
regexp_substr. Not sure if anyone can help ?
The question is, what is the difference between these two queries:
select regexp_substr('A1B2C3D4E', '[^0-9]+', 1, 3) from dual;
R
-
C
select regexp_substr('A1B2C3D4E', '[^0-9]*', 1, 3) from dual;
R
-
B
Why * and + gives different answers?
Thanks in advance
Alex
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