Test for numeric value?

Question

The vendor data we load in our staging table is rather dirty. One column in particular captures number data but 40% of the time has garbage characters or random strings.

Answer 1

WITH x (stringval) AS 
(
VALUES ('x2'),(''),('2.2.'),('5-'),('-5-'),('--5'),('.5'),('2 2'),('0.5-'),(' 1 '),('2  '),('3.'),('-4.0')
)
SELECT stringval,
CASE WHEN (

-- Whitespace must not appear in the middle of a number 
-- (but trailing and/or leading whitespace is permitted)
RTRIM(LTRIM( stringval )) NOT LIKE '% %'

-- A number cannot start with a decimal point
AND LTRIM( stringval ) NOT LIKE '.%'

-- A negative decimal number must contain at least one digit between 
-- the negative sign and the decimal point
AND LTRIM( stringval ) NOT LIKE '-.%'

-- The negative sign may only appear at the beginning of the number
AND LOCATE( '-', LTRIM(stringval)) IN ( 0, 1 )

-- A number must contain at least one digit
AND TRANSLATE( stringval, '0000000000', '123456789') LIKE '%0%'

-- Allow up to one negative sign, followed by up to one decimal point
AND REPLACE( 
    TRANSLATE( RTRIM(LTRIM(stringval)), '000000000', '123456789'), 
    '0', '') IN ('','-','.','-.')
)
THEN 'VALID'
ELSE 'INVALID'
END AS stringisvalidnumber
FROM x
;