assume that the current user_id = 1
uc table
prod_id / user_id
102 / 1
103 / 1cs table
prod_id / user_id
102 / 1I want to find out 103, that is, those data that are available in the uc table but not in the cs table
SELECT
uc.prod_id
FROM `user_cart` as uc
JOIN `user_cart_stock` as cs ON cs.prod_id = uc.prod_id
WHERE uc.user_id = 1
AND cs.prod_id IS NULLI find that writing like this doesn"t print anything?
you can change not in to not exists while using subqueries to optimize the query
select uc.prod_id from `uc`
where not exists (select `prod_id` from cs where prod_id=uc.prod_id); it is recommended to take a look at these four join- > left join,right join,inner join,out join.
there is no data because of your last condition
AND cs.prod_id IS NULLthis sentence leads to
look at the conditions you write are uc.user_id = 1 and cs.prod_id IS NULL , and they are inline queries, which cannot be queried.
:
SELECT uc.prod_id FROM `uc` as uc
LEFT JOIN `cs` as cs
ON cs.prod_id = uc.prod_id
WHERE uc.user_id = 1
AND cs.prod_id IS NULL
:
select uc.prod_id from `uc`
where `prod_id` not in (select `prod_id` from cs);Note that the table name is different from yours.
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