Obtenga el carácter entre los primeros 2 caracteres especiales en SQL

Este sería mi enfoque:

SELECT CAST('<x>' + REPLACE(data,'_','</x><x>') + '</x>' AS XML).value('/x[2]','int')
FROM YourTable

Primero transforma esto en un XML y luego selecciona el segundo nodo.

EDITAR:algunos ejemplos más en los que este enfoque es útil:

APLICACIÓN CRUZADA:puede usar este enfoque para obtener varios tokens a la vez

DECLARE @tbl TABLE(separated VARCHAR(100));
INSERT INTO @tbl VALUES('1_23:50_Look_this_is_a_test'),('2_12:00_that''s_one_more_test'),('3_13:30_great!_It_works!');

SELECT Converted.value('/x[1]','int') AS number
      ,Converted.value('/x[2]','time') AS time
      ,Converted.value('/x[3]','varchar(max)') AS text
FROM @tbl
CROSS APPLY(SELECT CAST('<x>' + REPLACE(separated,'_','</x><x>') + '</x>' AS XML) AS Converted) AS MySeparated
--type-safe and easy:
/*
number  time    text
1       23:50   Look
2       12:00   that's
3       13:30   great!
*/
GO

CTE:usar como parámetro

DECLARE @Parameter VARCHAR(100)='1_12:30_SomeValue';
WITH MyParameters AS
(
    SELECT CAST('<x>' + REPLACE(@Parameter,'_','</x><x>') + '</x>' AS XML).value('/x[1]','int') AS IntParam
          ,CAST('<x>' + REPLACE(@Parameter,'_','</x><x>') + '</x>' AS XML).value('/x[2]','time') AS TimeParam
          ,CAST('<x>' + REPLACE(@Parameter,'_','</x><x>') + '</x>' AS XML).value('/x[3]','varchar(max)') AS TextParam
)
SELECT IntParam,TimeParam,TextParam
FROM MyParameters
/*
IntParam    TimeParam   TextParam
1           12:30:00    SomeValue
*/
GO

Dividir cadena:transformar en lista

DECLARE @MyIDs VARCHAR(100)='3,5,7';
SELECT A.B.value('.','int') TheIntValue
FROM(SELECT CAST('<x>' + REPLACE(@MyIDs,',','</x><x>') + '</x>' AS XML) AS MyListAsXML) AS x
CROSS APPLY MyListAsXML.nodes('/x') AS A(B)

/*
TheIntValue
3
5
7
*/
GO

Declaración IN dinámica

DECLARE @tbl TABLE(ID INT,Content VARCHAR(max));
INSERT INTO @tbl VALUES(1,'Value 1'),(2,'Value 2'),(3,'Value 3'),(4,'Value 4'),(5,'Value 5'),(6,'Value 6'),(7,'Value 7');

DECLARE @MyIDs VARCHAR(100)='3,5,7';
/*
This won't work (due to the fact, that @MyIDs is not a list of INTs but a text
SELECT * FROM @tbl WHERE ID IN(@MyIDs)
*/
WITH AsList AS
(
    SELECT A.B.value('.','int') TheIntValue
    FROM(SELECT CAST('<x>' + REPLACE(@MyIDs,',','</x><x>') + '</x>' AS XML) AS MyListAsXML) AS x
    CROSS APPLY MyListAsXML.nodes('/x') AS A(B)

)
SELECT * FROM @tbl WHERE ID IN(SELECT TheIntValue FROM AsList)

/*
ID  Content
3   Value 3
5   Value 5
7   Value 7
*/