sql server - SQL Insert - Only insert on this condition -

i have table 1:

id    userstring   date      -------------------------  1    krbs         4/25/2014      2    wefg         4/24/2014 

and table 2:

id  userstring + other user info  ----------------------------------  1  krbs    +  . . .. .  

i'm preforming insert table 1 make condition insert if user available in table 2 (only insert row in table 1 if user exist in table2)

i'm doing 2 separate sql checks (one if user exist insert) i'm sure there better way

best way achieve define foreign key on table. simplest , implicit way it, reference on can found on msdn. means not ever able a) insert entry table if no corresponding fk exists, , b) delete base table if entries foreign key here (in case, delete user if has settings ). like:

alter table nameofthetable add constraint fk_somenameforthekey foreign key (nameofcolfromthistable)     references nameoftheothertable (nameofthecolumnyouarereferencing);