mysql：NOT IN查询语法问题

Question

why does this query doesn't return any result (it should return results)

SELECT id FROM T_CLIENT where id 
    not in (select distinct client_id from T_VENTE);

whereas this one does.

SELECT *
FROM T_CLIENT LEFT JOIN T_VENTE ON T_VENTE.client_id=T_CLIENT.id
WHERE T_VENTE.client_id IS NULL;

Those two queries seems the same to me.

Answer 1

The NOT IN query returns null. Instead use NOT EXISTS:

SELECT id FROM T_CLIENT c where NOT EXISTS  
    (select 1 from T_VENTE v where v.client_id = c.id);