(Hoping you meant for that reply to be on-list as I'm here responding on-list.)
On Mon, Mar 5, 2012 at 2:16 PM, A.M. <agentm@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Mar 4, 2012, at 9:13 PM, Chris Angelico wrote:
>
>> One of our tables has a few columns that may be interpreted as strings
>> or may be numbers (data type is varchar, numbers are stored as
>> decimal). Generally, operations are performed on the string, but
>> sometimes we need to parse out a number - without it failing on error.
>> I wrote the following function to approximate to the semantics of
>> atoi:
>
> I would recommend against such a schema since different data types should warrant their own columns, but if you are left with no choice...
The values have to be strings for other reasons (eg '' is valid
everywhere, and this is subsequently processed by a script that
expects all strings). So yeah, no choice there. But I agree that
normally you DO want integers stored in integer columns, and we're
paying a performance penalty for this.
>>
>> create or replace function str2int(val varchar) returns bigint immutable as $$
>> begin
>> val=substring(val from '[0-9]*');
>> if length(val) between 1 and 19 then return val::bigint; end if;
>> return 0;
>> end;
>> $$ language plpgsql;
>
> This can be written as:
> select substring('35345345.45645654' from '\d{1,19}')::bigint;
>
> Be aware that this does not account for:
> 3dogs
> 3 dogs
> 3,dogs
> 3.5.6.7
>
> all of which will return 3::bigint, but I assume that the column is not completely free-form or maybe this is what you want. (?)
>
> Cheers,
> M
That is in fact the behaviour I want. Trouble is, that simpler version
returns NULL if given 'asdf' as its input - I want it to return 0.
It's also about the same performance (slightly slower in a quick test)
than the original; it's still doing a regular expression parse. I was
hoping very much to avoid the regex altogether.
ChrisA
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