从文本字段中提取子字符串

Question

New to TSQL and SQL generally, please pardon if this is really basic:

I am working with a new-to-me-database that has ignored some best practices. Relevant to this discussion, some data is stored in a generalized note field, including loyalty numbers. The good news is that the loyalty numbers are at least stored consistently within the note.

So, a simplified example from the note table might be:

I have verified that every Loyalty Number is stored consistently ("Loyalty Number ####"), but obviously this is not ideal. I want to extract the Loyalty Number for every primary key that has them, then create a new field that stores the Loyalty Number.

What I'm having trouble with is the following: How do I run a query that will give me each primary key then, if there is a loyalty number return it, if not leave it null or say something like no result found. Eg, turn the above into something like.

It's trivially easy to construct something like "select primary_key, note from note_table where note like '%Loyalty Number%', but that doesn't do the job of clipping down to just the loyalty number (and leaving out extraneous text). The uniformity of the data means I could probably do this in Excel, but I'm wondering if it's possible in TSQL. Thanks in advance for your help.

Answer 1

Give something like this a try using case with substring and charindex :

select id,
    case when note like '%Loyalty Number [0-9][0-9][0-9][0-9]%'
        then 'Loyalty Number ' + 
             substring(note, 
                   charindex('Loyalty Number', note) + Len('Loyalty Number ') + 1, 4) 
    end as Note  
from note

• SQL Fiddle Demo

The case statement checks to see if Loyalty Number exists in the data. Substring splits the note field using charindex to find the starting position. This is hard coding a length of 4 characters for the loyalty number. Given your comments, this should work. If you have a dynamic number of characters, you'll need to modify this slightly.

Answer 2

Building on @ segeddes answer, here's the rest of the code, that will update your new LoyaltyNumber column.

Working SQL Fiddle: http://sqlfiddle.com/#!3/36e46/8

UPDATE note_table
SET LoyaltyNumber = 
        CASE 
            WHEN note LIKE '%Loyalty Number [0-9][0-9][0-9][0-9]%'
                THEN SUBSTRING(note, CHARINDEX('Loyalty Number', note) 
                 + LEN('Loyalty Number ') + 1, 4)
            ELSE 'Regular Customer'
        END 
FROM note_table

Table Definition and CRUD

CREATE TABLE note_table (
  id int identity(1,1), 
  Note VarChar(500),
  LoyaltyNumber varchar(20)
)

Insert Into note_table(Note) Values
('Customer Since 2012. Loyalty Number 4747'),
('Loyalty Number 2209'),
('Loyalty Number 2234.Customer Since 2009'),
('Pending Order');