How To Check Numerical Format in SQL Server 2008 - sql

Question

I am converting some existing Oracle queries to MSSQL Server (2008) and can't figure out how to replicate the following Regex check:
SELECT SomeField
FROM SomeTable
WHERE NOT REGEXP_LIKE(TO_CHAR(SomeField), '^[0-9]{2}[.][0-9]{7}$');
That finds all results where the format of the number starts with 2 positive digits, followed by a decimal point, and 7 decimal places of data: 12.3456789
I've tried using STR, CAST, CONVERT, but they all seem to truncate the decimal to 4 decimal places for some reason. The truncating has prevented me from getting reliable results using LEN and CHARINDEX. Manually adding size parameters to STR gets slightly closer, but I still don't know how to compare the original numerical representation to the converted value.
SELECT SomeField
, STR(SomeField, 10, 7)
, CAST(SomeField AS VARCHAR)
, LEN(SomeField )
, CHARINDEX(STR(SomeField ), '.')
FROM SomeTable
+------------------+------------+---------+-----+-----------+
| Orig | STR | Cast | LEN | CHARINDEX |
+------------------+------------+---------+-----+-----------+
| 31.44650944 | 31.4465094 | 31.4465 | 7 | 0 |
| 35.85609 | 35.8560900 | 35.8561 | 7 | 0 |
| 54.589623 | 54.5896230 | 54.5896 | 7 | 0 |
| 31.92653899 | 31.9265390 | 31.9265 | 7 | 0 |
| 31.4523333333333 | 31.4523333 | 31.4523 | 7 | 0 |
| 31.40208955 | 31.4020895 | 31.4021 | 7 | 0 |
| 51.3047869443893 | 51.3047869 | 51.3048 | 7 | 0 |
| 51 | 51.0000000 | 51 | 2 | 0 |
| 32.220633 | 32.2206330 | 32.2206 | 7 | 0 |
| 35.769247 | 35.7692470 | 35.7692 | 7 | 0 |
| 35.071022 | 35.0710220 | 35.071 | 6 | 0 |
+------------------+------------+---------+-----+-----------+

Answer 1

What you want to do does not make sense in SQL Server.
Oracle supports a number data type that has a variable precision:
if a precision is not specified, the column stores values as given.
There is no corresponding data type in SQL Server. You have have a variable number (float/real) or a fixed number (decimal/numeric). However, both apply to ALL values in a column, not to individual values within a row.
The closest you could do is:
where somefield >= 0 and somefield < 100
Or if you wanted to insist that there is a decimal component:
where somefield >= 0 and somefield < 100 and floor(somefield) <> somefield
However, you might have valid integer values that this would filter out.

Answer 2

This answer gave me an option that works in conjunction with checking the decimal position first.
SELECT SomeField
FROM SomeTable
WHERE SomeField IS NOT NULL
AND CHARINDEX('.', SomeField ) = 3
AND LEN(CAST(CAST(REVERSE(CONVERT(VARCHAR(50), SomeField , 128)) AS FLOAT) AS BIGINT)) = 7
While I understand this is terrible by nearly all metrics, it satisfies the requirements.
The basis of checking formatting on this data type in inherently flawed as pointed out by several posters, however for this very isolated use case I wanted to document the workaround.