this would be much easier if your types were correct :)
CREATE TABLE #table1 ( id1 INT, col1 VARCHAR(50) );
CREATE TABLE #table2
(
id2 VARCHAR(1)
, col2 VARCHAR(4)
);
INSERT INTO #table1
( id1
, col1
)
VALUES ( '1'
, '<a><b id="1"></b><b id="2"></b></a>'
);
INSERT INTO #table2
( id2, col2 )
VALUES ( '1', 'val1' ),
( '2', 'val2' );
;
WITH c AS ( SELECT id1
, col1 = CONVERT(XML, col1)
FROM #table1 t
)
SELECT id1
, col1
, id2
, col2
FROM c
CROSS APPLY c.col1.nodes('(/a/b)') q ( x )
LEFT JOIN #table2 t2 ON t2.ID2 = x.value('./@id', 'varchar(1)')
DROP TABLE #table1, #table2