cross-dbms начин да проверите дали низът е числов

По-долу са дадени три отделни реализации за всяка от SQL Server, MySQL и Oracle. Никой не използва (или не може) същия подход, така че изглежда няма кръстосано СУБД начин да го направите. За MySQL и Oracle се показва само обикновеният целочислен тест; за SQL Server се показва пълният числов тест.

За SQL Server:обърнете внимание, че isnumeric('.') връща 1.., но всъщност не може да бъде преобразуван във float. Някои текстове като „1e6“ не могат да бъдат преобразувани директно в числови, но можете да преминете през float и след това число.

;with tmp(x) as (
    select 'db01' union all select '1' union all select '1e2' union all
    select '1234' union all select '' union all select null union all
    select '1.2e4' union all select '1.e10' union all select '0' union all
    select '1.2e+4' union all select '1.e-10' union all select '1e--5' union all
    select '.' union all select '.123' union all select '1.1.23' union all
    select '-.123' union all select '-1.123' union all select '--1' union all
    select '---1.1' union all select '+1.123' union all select '++3' union all
    select '-+1.123' union all select '1 1' union all select '1e1.3' union all
    select '1.234' union all select 'e4' union all select '+.123' union all
    select '1-' union all select '-3e-4' union all select '+3e-4'  union all
    select '+3e+4' union all select '-3.2e+4' union all select '1e1e1' union all
    select '-1e-1-1')

select x, isnumeric(x),
    case when x not like '%[^0-9]%' and x >'' then convert(int, x) end as SimpleInt,
    case
    when x is null or x = '' then null -- blanks
    when x like '%[^0-9e.+-]%' then null -- non valid char found
    when x like 'e%' or x like '%e%[e.]%' then null -- e cannot be first, and cannot be followed by e/.
    when x like '%e%_%[+-]%' then null -- nothing must come between e and +/-
    when x='.' or x like '%.%.%' then null -- no more than one decimal, and not the decimal alone
    when x like '%[^e][+-]%' then null -- no more than one of either +/-, and it must be at the start
    when x like '%[+-]%[+-]%' and not x like '%[+-]%e[+-]%' then null
    else convert(float,x)
    end
from tmp order by 2, 3

За MySQL

create table tmp(x varchar(100));
insert into tmp
    select 'db01' union all select '1' union all select '1e2' union all
    select '1234' union all select '' union all select null union all
    select '1.2e4' union all select '1.e10' union all select '0' union all
    select '1.2e+4' union all select '1.e-10' union all select '1e--5' union all
    select '.' union all select '.123' union all select '1.1.23' union all
    select '-.123' union all select '-1.123' union all select '--1' union all
    select '---1.1' union all select '+1.123' union all select '++3' union all
    select '-+1.123' union all select '1 1' union all select '1e1.3' union all
    select '1.234' union all select 'e4' union all select '+.123' union all
    select '1-' union all select '-3e-4' union all select '+3e-4'  union all
    select '+3e+4' union all select '-3.2e+4' union all select '1e1e1' union all
    select '-1e-1-1';

select x,
    case when x not regexp('[^0-9]') then x*1 end as SimpleInt
from tmp order by 2

За Oracle

case when REGEXP_LIKE(col, '[^0-9]') then col*1 end