寻求sql语句

Question

表product_service:
 字段productid  serviceid
 
表product:
 字段itemid表service
 字段itemid现在要插入记录到product_service表中，插入条件：
假如service有记录：itemid
                   itemid1
                   itemid2
product有记录：
                   itemid
                   itemid11  
                   itemid22
                   itemid23
                   ........现在product_service中要插入：
productid  serviceid
itemid11   itemid1
itemid22   itemid1
itemid33   itemid1itemid11   itemid2
itemid22   itemid2
itemid33   itemid2

Answer 1

insert into product_service ( productid,serviceid )
select a.itemid,b.itemid from product a,service b

Answer 2

insert into product_service ( productid,serviceid )
select a.itemid,b.itemid from product_service a,service b