Regular expressions: splitting with REGEXP_SUBSTR and "null"

#11

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

#12

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

#13

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

#14

On Feb 29, 1:11*pm, spamb... (AT) milmac (DOT) com (Doug Miller) wrote:

Quote:

In article <248f35ac-1e8c-424a-80cd-1da3edc66... (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Pow... (AT) eds (DOT) com> wrote:

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.

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 returnsa
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.- Hide quoted text -

- Show quoted text -

Doug, valid point. I was not thinking about general cases only the
posted one and one should always be aware of what will break what you
wrote.

-- Mark D Powell --

#15

On Feb 29, 1:11*pm, spamb... (AT) milmac (DOT) com (Doug Miller) wrote:

Quote:

In article <248f35ac-1e8c-424a-80cd-1da3edc66... (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Pow... (AT) eds (DOT) com> wrote:

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.

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 returnsa
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.- Hide quoted text -

- Show quoted text -

Doug, valid point. I was not thinking about general cases only the
posted one and one should always be aware of what will break what you
wrote.

-- Mark D Powell --

#16

On Feb 29, 1:11*pm, spamb... (AT) milmac (DOT) com (Doug Miller) wrote:

Quote:

In article <248f35ac-1e8c-424a-80cd-1da3edc66... (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Pow... (AT) eds (DOT) com> wrote:

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.

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 returnsa
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.- Hide quoted text -

- Show quoted text -

Doug, valid point. I was not thinking about general cases only the
posted one and one should always be aware of what will break what you
wrote.

-- Mark D Powell --

#17

On Feb 29, 1:11*pm, spamb... (AT) milmac (DOT) com (Doug Miller) wrote:

Quote:

In article <248f35ac-1e8c-424a-80cd-1da3edc66... (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Pow... (AT) eds (DOT) com> wrote:

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.

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 returnsa
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.- Hide quoted text -

- Show quoted text -

Doug, valid point. I was not thinking about general cases only the
posted one and one should always be aware of what will break what you
wrote.

-- Mark D Powell --

#18

On 29 Feb, 20:11, spamb... (AT) milmac (DOT) com (Doug Miller) wrote:

Quote:

In article <248f35ac-1e8c-424a-80cd-1da3edc66... (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Pow... (AT) eds (DOT) com> wrote:

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:

SELECTREGEXP_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 aNull, so the string becomes
'One|Two||Four|'

the query

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

result in:
Four

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

Thank you in advance!

Will this help?

SQL> l
1 selectregexp_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 isNULL, but this method
returns 'five'. Conversely, trying to retrieve the fifth string should return
'five' but instead returnsNULL.

Also to return an actualNULLvalue
SQL> selectregexp_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 anullstring
- specifying the third substring in 'one|two||four|five' should return anull
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.

yes, you're right. maybe something more compact than that proposed by
Peter could be:

select
replace(
regexp_substr(replace('one|two||four','|','|\'),'[^|]+',1,4)
, '\', ''
) REG_RESULT
from dual;

where '\' should be a character that NEVER appears in "field" strings
(another one could be chosen)
it's an inelegant solution (or really ugly?), you should be really
sure it's never present

I wanted to learn regexp, but I think replace could be replaced
(sorry

with a regular expression...

thank you!

#19

On 29 Feb, 20:11, spamb... (AT) milmac (DOT) com (Doug Miller) wrote:

Quote:

In article <248f35ac-1e8c-424a-80cd-1da3edc66... (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Pow... (AT) eds (DOT) com> wrote:

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:

SELECTREGEXP_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 aNull, so the string becomes
'One|Two||Four|'

the query

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

result in:
Four

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

Thank you in advance!

Will this help?

SQL> l
1 selectregexp_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 isNULL, but this method
returns 'five'. Conversely, trying to retrieve the fifth string should return
'five' but instead returnsNULL.

Also to return an actualNULLvalue
SQL> selectregexp_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 anullstring
- specifying the third substring in 'one|two||four|five' should return anull
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.

yes, you're right. maybe something more compact than that proposed by
Peter could be:

select
replace(
regexp_substr(replace('one|two||four','|','|\'),'[^|]+',1,4)
, '\', ''
) REG_RESULT
from dual;

where '\' should be a character that NEVER appears in "field" strings
(another one could be chosen)
it's an inelegant solution (or really ugly?), you should be really
sure it's never present

I wanted to learn regexp, but I think replace could be replaced
(sorry

with a regular expression...

thank you!

#20

On 29 Feb, 20:11, spamb... (AT) milmac (DOT) com (Doug Miller) wrote:

Quote:

In article <248f35ac-1e8c-424a-80cd-1da3edc66... (AT) e6g2000prf (DOT) googlegroups.com>, Mark D Powell <Mark.Pow... (AT) eds (DOT) com> wrote:

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:

SELECTREGEXP_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 aNull, so the string becomes
'One|Two||Four|'

the query

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

result in:
Four

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

Thank you in advance!

Will this help?

SQL> l
1 selectregexp_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 isNULL, but this method
returns 'five'. Conversely, trying to retrieve the fifth string should return
'five' but instead returnsNULL.

Also to return an actualNULLvalue
SQL> selectregexp_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 anullstring
- specifying the third substring in 'one|two||four|five' should return anull
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.

yes, you're right. maybe something more compact than that proposed by
Peter could be:

select
replace(
regexp_substr(replace('one|two||four','|','|\'),'[^|]+',1,4)
, '\', ''
) REG_RESULT
from dual;

where '\' should be a character that NEVER appears in "field" strings
(another one could be chosen)
it's an inelegant solution (or really ugly?), you should be really
sure it's never present

I wanted to learn regexp, but I think replace could be replaced
(sorry

with a regular expression...

thank you!

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Regular expressions: splitting with REGEXP_SUBSTR and "null"

comp.databases.oracle.misc comp.databases.oracle.misc

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 03-01-2008 , 12:37 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 03-01-2008 , 12:37 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 03-01-2008 , 12:37 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 03-01-2008 , 09:21 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 03-01-2008 , 09:21 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 03-01-2008 , 09:21 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 03-01-2008 , 09:21 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 04-22-2008 , 06:31 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 04-22-2008 , 06:31 AM

Re: Regular expressions: splitting with REGEXP_SUBSTR and "null" - 04-22-2008 , 06:31 AM