Query to find if a column contains both number and decimal only - sql

Question

I have a column to check if contains number from 0-9 and a decimal. Since in the version of SQL am using the below does not seem working
select *
from tablename
whwere columnname like '%[^.0-9]%'
Also tried using column name like '%[0-9]%' and columnname not like '%.%' but if there is a negative sign it is not getting captured. Please advise.
The column data type is float. So can someone provide me a query to check if the column contains values from 0-9 and also it can contain decimal values these two are permitted. If say for example if I have value 9,9.99 ,-1.24 the query should output -1.24 I need this value other than decimal and number –

Answer 1

The issue with your LIKE clause is bad predicate logic ...like '%[^.0-9]%'should be NOT LIKE '%[^0-9.]%'
Take this sample data.
DECLARE #table TABLE (SomeNbr VARCHAR(32));
INSERT #table VALUES ('x'),('0'),('0.12'),('999'),('-29.33'),('88.33.22'),('9-9-'),('11-');
What you were trying to do would be accomplished like this:
SELECT t.someNbr
FROM #table AS t
WHERE someNbr NOT LIKE '%[^0-9.]%';
The problem here is we'll also return "88.33.22" and miss "-29.33", both valid float values. You can handle hyphens by adding a hyphen to your LIKE pattern:
SELECT t.someNbr, LEN(t.SomeNbr)-LEN(REPLACE(t.SomeNbr,'.',''))
FROM #table AS t
WHERE someNbr NOT LIKE '%[^0-9.-]%';
But now we also pick up "9-9-" and stuff with 2+ dots. To ensure that each starts with a number OR a hyphen, to ensure hyphens only exist in the front of the string (if at all) and that we a maximum of one dot:
--==== This will do a good job but can still be broken
SELECT t.someNbr
FROM #table AS t
WHERE someNbr NOT LIKE '%[^0-9.-]%' -- Can only contain numbers, dots and hyphens
AND LEN(t.SomeNbr)-LEN(REPLACE(t.SomeNbr,'.','')) < 2 -- can have up to 1 dot
AND LEN(t.SomeNbr)-LEN(REPLACE(t.SomeNbr,'-','')) < 2 -- can have up to 1 hyphen
AND PATINDEX('%-%',t.SomeNbr) < 2 -- hyphen can only be in the front
This does the trick and returns:
someNbr
--------------------------------
0
0.12
999
-29.33
All that said - **DONT DO THIS ANY OF THIS ^^^ **. There is no need to parse numbers in this way except to show others why not to. I can still break this. They way I return valid floats in a scenario like this is with TRY_CAST or TRY_CONVERT. This returns what you need and will perform better.
--==== Best Solution
SELECT t.someNbr
FROM #table AS t
WHERE TRY_CAST(t.SomeNbr AS float) IS NOT NULL;