MySQL查询会删除A表中未在B表上找到ID的所有行？

Question

In my mySQL database, under the table audience there is a column called unique_hash where it has unique identifiers for each of my visitors.

In the table behaviour there is a column unique_hash and page . A unique_hash can have many rows, contrary to the audience table. However, the unique_hash found on behaviour are from the visitors that already saved them into the audience table.

Unfortunately for some maintenace reasons, I lost some of my data, and the result is that the distinct number of unique_hash in table behaviour are more than the unique hash of audience , the time that this should be equal.

What is the mysql query that will delete all the rows in the behaviour table where the unique_hash are not found on the audience table?

Answer 1

You can use NOT IN like the following:

DELETE FROM behaviour 
WHERE NOT unique_hash IN (
    SELECT DISTINCT unique_hash FROM audience
)

A second solution would be to use NOT EXISTS :

DELETE FROM behaviour
WHERE NOT EXISTS (
    SELECT * FROM audience 
    WHERE audience.unique_hash = behaviour.unique_hash
)