推荐系统核心部分
INSERT INTO recommend (
SELECT ut.userid,it.itemid, NOW() FROM user_tag ut,item_tag it WHERE
EXISTS
(
SELECT it.tagid FROM item_tag it WHERE it.tagid IN (SELECT ut.tagid FROM user_tag ut)
)
)
INSERT INTO recommend (
SELECT ut.userid,it.itemid, NOW() FROM user_tag ut,item_tag it WHERE
EXISTS
(
SELECT it.tagid FROM item_tag it WHERE EXISTS (SELECT ut.tagid = it.tagid FROM user_tag ut,item_tag it)
)
)
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