Joining on an XML attribute

Question

I have some xml stored in an varchar column and the id in the attributes of some of those nodes is a key in another table. How can I do a join on multiple attributes? I know the value method below only returns one id (and the first one at that).

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');

select * from #table1 t1
left join #table2 t2 on t2.id2 = cast(t1.col1 as xml).value('(/a/b/@id)[1]', 'varchar(1)')

Returns

id1  col1                                   id2 col2
1    <a><b id="1"></b><b id="2"></b></a>    1   val1

How can I get another row returned for table2's ID 2?

1    <a><b id="1"></b><b id="2"></b></a>    2   val2

Answer 1

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