forma cruzada de dbms para verificar si la cadena es numérica

A continuación se muestran tres implementaciones separadas para cada uno de SQL Server, MySQL y Oracle. Ninguno usa (o puede) el mismo enfoque, por lo que no parece haber una forma cruzada de DBMS para hacerlo. Para MySQL y Oracle, solo se muestra la prueba de entero simple; para SQL Server, se muestra la prueba numérica completa.

Para SQL Server:tenga en cuenta que isnumeric('.') devuelve 1... pero en realidad no se puede convertir a flotante. Algunos textos como '1e6' no se pueden convertir a numéricos directamente, pero se pueden pasar a flotante y luego a numérico.

;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

Para 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

Para oráculo

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