select specific rows sql server xml buttress type

i'm perplexing name information list tangible identical following :

column     |    information type
-------------------------
id         |    int
datatype   |    int
loggeddata |    xml

but i wholly wish name those rows specific datatype value, enclose twine (or evaluates square xpath) loggeddata column.

a discerning google hunt incited adult zero useful, i am bit rush an answer... i'll lift searching, nonetheless anyone assistance me out meant time, i'd unequivocally conclude it.

edit _ clarification

so, i'm after something this, nonetheless repremand format...

select id, loggeddata mytable where datatype = 29 loggeddata.query('rootnode/ns1:childnode[@value="searchterm"]');

still competence clear...