Postgres query to check a string is a number

Question

Can anyone tell me the query to check whether a string is a number(double precision). It should return true if the string is number. else it should return false.

con

Answer 1

I think the easiest way would be a regular expression match:

select '12.41212' ~ '^[0-9\.]+$'
=> true

select 'Service' ~ '^[0-9\.]+$'
=> false

Answer 2

If you want to check with exponential , +/- . then the best expression is :

^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$

resulting in:

select '12.41212e-5' ~ '^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$' ;

as true.

The expression is from: https://www.regular-expressions.info/floatingpoint.html

You can check for other types of numbers, for example if you expect decimal, with a sign.

 select '-12.1254' ~ '^[-+]?[0-9]*\.?[0-9]+$';

Answer 3

select s1 ~ '^\d+$';
select s2 ~ '^\d+$';

Answer 4

I fixed the regular expression that a_horse_with_no_name has suggested.

SELECT '12.41212' ~ '^\d+(\.\d+)?$'; -- true
SELECT 'Service' ~ '^\d+(\.\d+)?$'; -- false

Answer 5

If you only need to accept double precision numbers, this should work fine:

select '12.41212' ~ '^\d+\.?\d+$'; -- true
select 'Service' ~ '^\d+\.?\d+$'; -- false

This would also accept integers, and negative numbers:

select '-1241212' ~ '^-?\d+\.?\d+$'; -- true

Answer 6

I would like to propose another suggestion, since 12a345 returns true by ns16's answer.

SELECT '12.4121' ~ '^\d+(\.\d+)?$'; #true
SELECT 'ServiceS' ~ '^\d+(\.\d+)?$'; #false
SELECT '12a41212' ~ '^\d+(\.\d+)?$'; #false
SELECT '12.4121.' ~ '^\d+(\.\d+)?$'; #false
SELECT '.12.412.' ~ '^\d+(\.\d+)?$'; #false