How to extract the specific substrings from a single string?

Question

I have a string that I need to break apart for codes.

String examples - 'H345678_30', 'q789038_155'

To extract the code after the underscore I have something that works

  Select Code = RIGHT(@temp ,CHARINDEX('_',REVERSE(@temp)) - 1)

The code I'm having a hard time extracting is from the first part before the '_'. Lets say we take 'H345678_30', the first 3 characters are always Precodes like H34 or in the other example as mentioned aboved it will be Q78. The #s that follow after H34 and end before '_' is what I need.

In this case it will be 5678.

So far I have this but any suggestions to make this work more efficiently it will be great

Select TCode = LEFT((SUBSTRING(@temp,Charindex('q',@temp)+3,Len(@temp))), (charindex('_', ((SUBSTRING(@temp,Charindex('q',@temp)+3,Len(@temp))))))-1)

Thank you

Answer 1

如果前三个字符始终是“预编码”，则可以简单地执行以下操作：

SELECT SUBSTRING('H345678_30',4,CHARINDEX('_','H345678_30')-4)

Answer 2

You can try following code, I have captured everything that is on left side of '_' character and then I have removed first 3 characters to get 5678:

DECLARE @x VARCHAR(max) = 'H345678_30'
SELECT SUBSTRING(LEFT(@x, CHARINDEX('_', @x)-1), 4, 10)