Question

I have two columns (A, B) like this….

A           B
12_18_19    20

I want a 3rd column (C) added within same SELECT statement like this…

C
12_18_20_19

in other words, my column A is delimited by “_”, so the second last index of column A should be column B.

If possible I would do do all this within same SELECT statement like this…

A         B    C
12_18_19  20   12_18_20_19

Answer 1

How about:

SELECT 
    A, B, 
    C = SUBSTRING(A, 1, LEN(A) - CHARINDEX('_', REVERSE(A))) + 
        '_' + B + 
        SUBSTRING(A, LEN(A) + 1 - CHARINDEX('_', REVERSE(A)), 999)
FROM 
    dbo.YourTable 

It’s a bit involved, mostly also because there is no LASTCHARINDEX() function in T-SQL.

The first expression parses the A column up to the last _ separator characters and takes everything before that. Then it appends a _ and column B, and then grabs everything after that last _ separator from A and appends that.

And as Andriy M rightfully mentioned in his comment : if A or B are NULL, then the whole result is NULL, too. If the columns are empty strings, or if A doesn’t contain any _ characters, you’ll might get errors (since the parsing will fail) or unexpected, messy results.