A Table
a_id
title
B Table
b_id
a_id
user_id
baomin
Table An is the active table, and Table B is the registration form
current user user_id equals 7
the requirement is to show all the activities that the current user has not signed up for and how to write the mysql statement, gods.
explain only concepts
select from a left join b on where b_id is null
or
select from a where a_id not in (select a_id from b)
SELECT a.* FROM a
WHERE NOT EXISTS(SELECT b.ID from b where a. a_id = b.a_id AND b. user_id = 7)try this
through a subquery-sharp table_aAtable_bB
SELECT a_id 'ID', title '' FROM table_a WHERE a_id NOT IN (SELECT a_id FROM table_b WHERE user_id = 7);Previous: IDEA keeps flashing updating indices.
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