SQLITE select only numeric values from text field - vb.net

Question

In VB .net I'm wanting to run an sqlite select statement to fetch only numeric values from a text field (a4) which contains both numbers and letters.
My sqlite text a4 field data contains data like this:
28 days
1966
the 100 years war
In would like to be able to fetch
28
1966
100
The sqlite a4 field has a text data type
This is what I have tried
SELECT a4 from data where CAST(a4 AS INTEGER) GLOB '[0-9]'
SELECT a4 FROM data WHERE a4 REGEXP '[0-9]'
I have search for an answer but only found MS SQL answer that uses ISNUMERIC which doesn't exist in SQLITE.
Thanks

Answer 1

You can do it in SQL for SQLite3:
SELECT ROUND(a4) from data WHERE NOT ROUND(a4) = 0;
This is because non-numeric values applied to the ROUND() function result in a value of 0. For example:
sqlite> select round('hello');
round('hello')
--------------
0.0
..whereas numeric values stored as text become numbers:
sqlite> select round('1234');
round('1234')
-------------
1234.0
N.B. There is a limitation to this solution is if a numeric value is also '0' or rounds to 0.0, such as text value '0.1'. It also will give a false positive if the text starts with a number but includes other characters, e.g.
sqlite> select round('1234Hello');
round('1234Hello')
------------------
1234.0

Answer 2

Not done in the database but in the client code.
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim strings() As String = {"28 days", "1966", "the 100 years war"}
Dim numbers As New List(Of String)
For Each s In strings
Dim num As String = ""
For Each c As Char In s
If Char.IsNumber(c) Then
num &= c
End If
Next
numbers.Add(num)
Next
For Each num In numbers
Debug.Print(num)
Next
'28
'1966
'100
End Sub