PostgreSQL - regex issue

Question

I'm trying the following instruction and I don't understand the TRUE value returned :

SELECT '1' ~ '(0[1-9])|[10-15]' ;

?column?
boolean
----------
t

If I make it simplier again, I still don't understand the value returned :

SELECT '1' ~ '[10-15]' ;

?column?
boolean
----------
t

Thank you for helping !

Thomas

i think you could use SELECT '1' ~ '(0[1-9])|(1[0-5])';

Vivek S.
– Vivek S.

2014-07-10 07:27:49 +00:00
Commented Jul 10, 2014 at 7:27 — Vivek S.
– Vivek S., Commented Jul 10, 2014 at 7:27

mu is too short · Accepted Answer · 2014-07-10 07:09:36Z

4

This regex:

[10-15]

doesn't mean what you think it means. The things inside a character class (i.e. [...]) are individual characters, not strings. So that regex matches a '1', anything between '0' and '1', or a '5'; simplifying, we have [015]. In particular, that regex does not match anything between '10' and '15' as you seem to think.

I think you're looking for:

(0[1-9])|(1[0-5])

You just need to factor out the '1' in the second part of the alternation in the same way that you factored out the '0' in the first part.

answered Jul 10, 2014 at 7:09

mu is too short

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1 Comment

wiltomap Over a year ago

That's it, thank you so much ! I didn't understand that... It is perfectly clear now. Have a good day.

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