regex function using only a single quote - oracle

Question

I want to select with regex if the column has one single quote only.
Example..
Column1: who's responsible of this
Column2: who''s responsible of this
With this query
Select regexp_substr(column1,'''') from ex_tab
will always consider colum2 that have one single quote but actually it has 2
I want to select only one single quote not the doubles
I cannot use instr function because i might have who's responsible of the's

Answer 1

Um, you can certainly use INSTR to do this:
with str as (select 'who''s in charge?' col1 from dual union all
select 'who''''s in charge?' col1 from dual union all
select 'who''s in charge? I''m in charge!' col1 from dual union all
select 'who is in charge?' col1 from dual union all
select 'who''''s in charge? I''''m in charge!' from dual)
select col1,
case when instr(col1, '''''', 1) != 0 then 'no' else 'yes' end is_ok
from str;
COL1 IS_OK
--------------------------------- -----
who's in charge? yes
who''s in charge? no
who's in charge? I'm in charge! yes
who is in charge? yes
who''s in charge? I''m in charge! no
It'll most likely be faster than the regexp way.

Answer 2

You can negate characters in set using [^].
Some manual. I just noticed that there is no info there that ^ sign as first character in square brackets means "not in this set".
So regexp like:
^('?([^']+'[^']+'?)?)*$
should match everything that do not have two quotes one after another in it. And match single quote. And match strings that have more than one quote, separated by another string.
So, to put it as complete example, what Your want wloud be:
Select
column1,
REGEXP_COUNT(column1,'^(''?([^'']+''[^'']+''?)?)*$')
from
(
select 'who''''s responsible of this' as column1 FROM dual
union
select 'who''s responsible of this' as column1 FROM dual
union
select 'who''s responsible ''of'' this' as column1 FROM dual
union
select '''who''s responsible ''of'' this' as column1 FROM dual
union
select '''' as column1 FROM dual
)
Where is_ok column indicates wether the value contains two quotes, or not.
EDIT:
I just realized that there is much simpler solution. Just check if there are two or more occurances of quotes one after another. So, regexp would be just:
'{2,}
and here is working example, be aware of changing name of column to is_not_ok:
Select
column1,
REGEXP_COUNT(column1,'''{2,}') as is_not_ok
from
(
select 'who''''s responsible of this' as column1 FROM dual
union
select 'who''s responsible of this' as column1 FROM dual
union
select 'who''s responsible ''of'' this' as column1 FROM dual
union
select '''who''s responsible ''of'' this' as column1 FROM dual
union
select '''' as column1 FROM dual
union
select 'this''' as column1 FROM dual
union
select '''''' as column1 FROM dual
)