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  #1  
Old   
citte
 
Posts: n/a

Default Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-28-2008 , 10:02 AM





Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!

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  #2  
Old   
Mark D Powell
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 11:31 AM





On Feb 28, 11:02*am, citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Quote:
Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!
Will this help?

SQL> l
1 select regexp_substr(replace('one|two||four','||','|NULL| '),
2* '[^|]+',1,3) from dual
SQL> /

REGE
----
NULL

Also to return an actual NULL value
SQL> select regexp_substr(replace('one|two||four','||',''),
2 '[^|]+',1,3) from dual;

R
-


HTH -- Mark D Powell --


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  #3  
Old   
Mark D Powell
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 11:31 AM


On Feb 28, 11:02*am, citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Quote:
Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!
Will this help?

SQL> l
1 select regexp_substr(replace('one|two||four','||','|NULL| '),
2* '[^|]+',1,3) from dual
SQL> /

REGE
----
NULL

Also to return an actual NULL value
SQL> select regexp_substr(replace('one|two||four','||',''),
2 '[^|]+',1,3) from dual;

R
-


HTH -- Mark D Powell --


Reply With Quote
  #4  
Old   
Mark D Powell
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 11:31 AM


On Feb 28, 11:02*am, citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Quote:
Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!
Will this help?

SQL> l
1 select regexp_substr(replace('one|two||four','||','|NULL| '),
2* '[^|]+',1,3) from dual
SQL> /

REGE
----
NULL

Also to return an actual NULL value
SQL> select regexp_substr(replace('one|two||four','||',''),
2 '[^|]+',1,3) from dual;

R
-


HTH -- Mark D Powell --


Reply With Quote
  #5  
Old   
Mark D Powell
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 11:31 AM


On Feb 28, 11:02*am, citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Quote:
Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!
Will this help?

SQL> l
1 select regexp_substr(replace('one|two||four','||','|NULL| '),
2* '[^|]+',1,3) from dual
SQL> /

REGE
----
NULL

Also to return an actual NULL value
SQL> select regexp_substr(replace('one|two||four','||',''),
2 '[^|]+',1,3) from dual;

R
-


HTH -- Mark D Powell --


Reply With Quote
  #6  
Old   
Doug Miller
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 12:11 PM


In article <248f35ac-1e8c-424a-80cd-1da3edc66966 (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Powell (AT) eds (DOT) com> wrote:
Quote:
On Feb 28, 11:02=A0am, citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!

Will this help?

SQL> l
1 select regexp_substr(replace('one|two||four','||','|NULL| '),
2* '[^|]+',1,3) from dual
SQL> /

REGE
----
NULL
Doesn't work in a more general case, e.g. attempting to select the fourth
string from 'one|two|||five' -- the desired result is NULL, but this method
returns 'five'. Conversely, trying to retrieve the fifth string should return
'five' but instead returns NULL.
Quote:
Also to return an actual NULL value
SQL> select regexp_substr(replace('one|two||four','||',''),
2 '[^|]+',1,3) from dual;

R
-
Also doesn't work for more general cases:
- specifying the second substring should return 'two' but instead returns
'twofour'
- specifying the fourth substring should return 'four' but instead returns a
null string
- specifying the third substring in 'one|two||four|five' should return a null
string, but instead returns 'five'

In general, when seeking the i-th substring, if the omitted substring is in
the n-th position, this method is guaranteed to produce correct results only
when 0 < i < (n - 1), or when i = n AND there are at most n non-null
substrings. If there are multiple omitted substrings, correct results may also
be obtained for other values of i, but only by coincidence.


Reply With Quote
  #7  
Old   
Doug Miller
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 12:11 PM


In article <248f35ac-1e8c-424a-80cd-1da3edc66966 (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Powell (AT) eds (DOT) com> wrote:
Quote:
On Feb 28, 11:02=A0am, citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!

Will this help?

SQL> l
1 select regexp_substr(replace('one|two||four','||','|NULL| '),
2* '[^|]+',1,3) from dual
SQL> /

REGE
----
NULL
Doesn't work in a more general case, e.g. attempting to select the fourth
string from 'one|two|||five' -- the desired result is NULL, but this method
returns 'five'. Conversely, trying to retrieve the fifth string should return
'five' but instead returns NULL.
Quote:
Also to return an actual NULL value
SQL> select regexp_substr(replace('one|two||four','||',''),
2 '[^|]+',1,3) from dual;

R
-
Also doesn't work for more general cases:
- specifying the second substring should return 'two' but instead returns
'twofour'
- specifying the fourth substring should return 'four' but instead returns a
null string
- specifying the third substring in 'one|two||four|five' should return a null
string, but instead returns 'five'

In general, when seeking the i-th substring, if the omitted substring is in
the n-th position, this method is guaranteed to produce correct results only
when 0 < i < (n - 1), or when i = n AND there are at most n non-null
substrings. If there are multiple omitted substrings, correct results may also
be obtained for other values of i, but only by coincidence.


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  #8  
Old   
Doug Miller
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 12:11 PM


In article <248f35ac-1e8c-424a-80cd-1da3edc66966 (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Powell (AT) eds (DOT) com> wrote:
Quote:
On Feb 28, 11:02=A0am, citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!

Will this help?

SQL> l
1 select regexp_substr(replace('one|two||four','||','|NULL| '),
2* '[^|]+',1,3) from dual
SQL> /

REGE
----
NULL
Doesn't work in a more general case, e.g. attempting to select the fourth
string from 'one|two|||five' -- the desired result is NULL, but this method
returns 'five'. Conversely, trying to retrieve the fifth string should return
'five' but instead returns NULL.
Quote:
Also to return an actual NULL value
SQL> select regexp_substr(replace('one|two||four','||',''),
2 '[^|]+',1,3) from dual;

R
-
Also doesn't work for more general cases:
- specifying the second substring should return 'two' but instead returns
'twofour'
- specifying the fourth substring should return 'four' but instead returns a
null string
- specifying the third substring in 'one|two||four|five' should return a null
string, but instead returns 'five'

In general, when seeking the i-th substring, if the omitted substring is in
the n-th position, this method is guaranteed to produce correct results only
when 0 < i < (n - 1), or when i = n AND there are at most n non-null
substrings. If there are multiple omitted substrings, correct results may also
be obtained for other values of i, but only by coincidence.


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  #9  
Old   
Doug Miller
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 12:11 PM


In article <248f35ac-1e8c-424a-80cd-1da3edc66966 (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Powell (AT) eds (DOT) com> wrote:
Quote:
On Feb 28, 11:02=A0am, citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Hi,
I have a problem, I found on internet a way to split strings separated
by pipe | (for example) with regexp, something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated by the pipe
is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?

Thank you in advance!

Will this help?

SQL> l
1 select regexp_substr(replace('one|two||four','||','|NULL| '),
2* '[^|]+',1,3) from dual
SQL> /

REGE
----
NULL
Doesn't work in a more general case, e.g. attempting to select the fourth
string from 'one|two|||five' -- the desired result is NULL, but this method
returns 'five'. Conversely, trying to retrieve the fifth string should return
'five' but instead returns NULL.
Quote:
Also to return an actual NULL value
SQL> select regexp_substr(replace('one|two||four','||',''),
2 '[^|]+',1,3) from dual;

R
-
Also doesn't work for more general cases:
- specifying the second substring should return 'two' but instead returns
'twofour'
- specifying the fourth substring should return 'four' but instead returns a
null string
- specifying the third substring in 'one|two||four|five' should return a null
string, but instead returns 'five'

In general, when seeking the i-th substring, if the omitted substring is in
the n-th position, this method is guaranteed to produce correct results only
when 0 < i < (n - 1), or when i = n AND there are at most n non-null
substrings. If there are multiple omitted substrings, correct results may also
be obtained for other values of i, but only by coincidence.


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  #10  
Old   
Peter Nilsson
 
Posts: n/a

Default Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 02-29-2008 , 11:37 PM


citte <nicola.ame... (AT) gmail (DOT) com> wrote:
Quote:
Hi,
I have a problem, I found on internet a way to split
strings separated by pipe | (for example) with regexp,
something like that:

SELECT REGEXP_SUBSTR('One|Two|Three|Four','[^|]+', 1, 3)
FROM dual;

which gives the result:
Three

the problem comes when I have one of the words separated
by the pipe is actually a Null, so the string becomes
'One|Two||Four|'

the query

SELECT REGEXP_SUBSTR('One|Two||Four','[^|]+', 1, 3)
FROM dual;

result in:
Four

I needed a Null (or empty string).
How is this possible?
Here are some (not necessarily pretty) ways, assuming n > 0...

select
x,
n,
substr(
'|' || x || '|',
instr('|' || x || '|', '|', 1, n) + 1,
instr('|' || x || '|', '|', 1, n + 1)
- instr('|' || x || '|', '|', 1, n) - 1),
regexp_replace(
'|' || x || '|',
'^([^\|]*\|){' || n || ',' || n || '}([^\|]*)|.*',
'\2' ),
regexp_substr(
regexp_substr(x || '|', '[^\|]*\|', 1, n),
'[^\|]*'),
regexp_substr(
'|' || x,
'[^\|]*',
instr('|' || x, '|', 1, n) + 1)
from
(select 'one|two||four|five' x from dual),
(select level n from dual connect by level <= 7)

--
Peter


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