检查字符串是否仅包含数字

Question

I am trying to check if a string contains only valid number in the following format

123.456
123
.356

But it should reject anything that contains non-numbers including double dots. Here are some invalid formats

d123.456
123d
12d3
d.1256
12d.456
12.d12
12.d45d
12.45.56

I have done the following

SELECT CASE WHEN '123.00' NOT LIKE '%[^0-9.]%' THEN 'Valid' ELSE 'Invalid' END

When seems to work except for the case where there is more than one dot in the string.

How can I tweak the regular expression to only allow one dot otherwise return 'Invalid'?

Answer 1

I would suggest try_convert() :

select (case when try_convert(col, float) is not null then 'valid' else 'invalid' end)

The one possible downside is exponential format; 1e6 is a valid number for instance.

An alternative is the where approach; you just need more complete logic:

select (case when col like '%[^0-9.]%' then 'invalid'
             when col like '%.%.%' then 'invalid'
             else 'valid'
        end)

Answer 2

TRY_PARSE will let you compare the input value to any/all numeric datatypes you decide to allow -- for example:

SELECT 
   TRY_PARSE('123.456' as int) as [int],
   TRY_PARSE('123.0' as float) as [float],
   TRY_PARSE('d123.456' as int) as [int],
   TRY_PARSE('d123.456' as float) as [float]

FWIW -- ISNUMERIC is often suggested, and is certainly the best- sounding function name :-) -- but doesn't work the way most folks seem to expect. (It allows math and currency symbols, etc.)

Answer 3

有一个内置的 sql server 函数：

Select CASE WHEN isnumeric([fieldname]) THEN 'Valid' ELSE 'Invalid" END

Answer 4

If you're not tied to regular expressions, SQL Server has an ISNUMERIC function you can use for this.

ISNUMERIC returns 1 when the input expression evaluates to a valid numeric data type; otherwise it returns 0.

Answer 5

Alternative solution for NOT LIKE clause is:

where REGEXP_LIKE(column, '^[[:digit:]]+$')