Extract substring from a string in SQL Server

问题

I need to extract a part of substring from string which follows as per below.

YY_12.Yellow
ABC_WSA.Thisone_A
SS_4MON.DHHE_A_A

I need to extract the string as per below

Yellow
Thisone
DHHE

回答1:

You could use something like this:

declare @tbl table (col nvarchar(100));
insert @tbl values ('YY_12.Yellow'), ('ABC_WSA.Thisone_A'), ('SS_4MON.DHHE_A_A')

select *
    , charindex('_', col2, 0)
    , left(col2, 
               case 
                   when charindex('_', col2, 0) - 1 > 0 
                       then charindex('_', col2, 0) - 1 
                   else len(col2) 
               end) [result]
from (
select col
    , substring(col, charindex('.', col, 0) + 1, len(col)) [col2]
from @tbl ) rs

I'm going to leave the full code so as you can hopefully understand what I did.

First identify and remove everything up to the dot "." (in the [col2] column in the nested SELECT)
Then I nest that SELECT so I can apply a new logic much easier on the result column from the first SELECT from which I only keep everything up to the underscore "_"
The final result is stored in the [result] column

回答2:

Try this:

CREATE TABLE app (info varchar(20))
INSERT INTO app VALUES
('YY_12.Yellow'),
('ABC_WSA.Thisone_A'),
('SS_4MON.DHHE_A_A'),
('testnopoint')

SELECT 
    CASE
        WHEN CHARINDEX('.', info) > 0 THEN 
        CASE 
            WHEN CHARINDEX('_', info, CHARINDEX('.', info) + 1) > 0 THEN
            SUBSTRING(info, CHARINDEX('.', info) + 1, CHARINDEX('_', info, CHARINDEX('.', info) + 1) - CHARINDEX('.', info) - 1)
            ELSE
            SUBSTRING(info, CHARINDEX('.', info) + 1, LEN(info))
         END
    END
FROM app

My query, if . is not present returns NULL, if you want returns all string remove the CASE statement

Go on SqlFiddle

回答3:

You could also try with parsename() function available from SQL Server 2012

select Name, left(parsename(Name,1), 
                 case when charindex('_', parsename(Name,1)) > 0 
                      then charindex('_', parsename(Name,1))-1 
                      else len(parsename(Name,1)) 
                 end) [ExtrectedName] from table

This assumes you have always . in your string to read the name after .

Result :

Name              ExtrectedName
YY_12.Yellow      Yellow
ABC_WSA.Thisone_A Thisone
SS_4MON.DHHE_A_A  DHHE

回答4:

Try this, used STUFF here

SELECT  LEFT(STUFF(col,1,CHARINDEX('.',col),''),
                CHARINDEX('_',STUFF(col,1,CHARINDEX('.',col),'')+'_')-1
            )
FROM    @table

Output:-

Yellow
Thisone
DHHE

来源：https://stackoverflow.com/questions/48185814/extract-substring-from-a-string-in-sql-server

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sql

sql-server

tsql