There are 2 tables in MySQL .
the first
id 1 2 3 4 и т.д. The second
product_id 2 4 и т.д. If the id from one table and product_id from the second, then this id should not be included in the selection from the first table.
1 answer
SELECT * FROM table_a a -- Выбираем все из table_a LEFT JOIN products p -- Ищем соответствующую строку в products ON a.id = p.product_id -- (но не выкидываем строки table_a без соответствия) WHERE p.product_id is null -- Оставляем только строки без соответствующего продукта. In general, there are three options: JOIN vs NOT EXISTS vs NOT IN, slightly different in semantics, as well as in performance.
Nickolay Nickolay
1,190 four 22
- And how do performance compare? - splash58
- A long essay is not ready to write, if a short answer, then in MySQL it seems like JOIN is better: phpfaq.ru/where_exists , spin.atomicobject.com/2011/03/25/mysql-in-query-performance , but this is a feature of the implementation. - Nickolay
- Thank. Hard about where in. And I would use them in a similar case - splash58
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