Extracting Portions of String - substring

Question

I have a field with the following types of string
X000233756_9981900025_201901_EUR_/
I firstly need to take take the characters to the left of the first _
Secondly I need to take the characters between the first and 2nd _
First _ is CHARINDEX('_',[Line_Item_Text],1) AS Position_1
Second _ is CHARINDEX('_',[Line_Item_Text],CHARINDEX('_',[Line_Item_Text],1)+1) AS Position_2
I was then expecting to be able to do
left([Line_Item_Text],CHARINDEX('_',[Line_Item_Text],1)-1) AS Data_1
Substring([Line_Item_Text],CHARINDEX('_',[Line_Item_Text],1)+1),CHARINDEX('_',[Line_Item_Text],CHARINDEX('_',[Line_Item_Text],1)+1) - CHARINDEX('_',[Line_Item_Text],1)+1)) AS Data_2"
Which should give me
X000233756
9981900025
But getting errors with incorrect number of functions when I start adding and subtracting from CHARINDEX Function.
Any ideas where I am going wrong?
TIA
Geoff

Answer 1

Actually, using the base string functions here is going to be an ugly nightmare. You might find that STRING_SPLIT along with some clever logic might be easier:
SELECT value
FROM STRING_SPLIT('X000233756_9981900025_201901_EUR_', '_')
WHERE LEN(value) > 6 AND NOT value LIKE '[A-Z]%';
This answer assumes that the third and fourth components would always be a 6 digit date and 3 letter currency code, and that the first (but not second) component would always start with some letter.
Demo