MySQL, merging 2 or more tables before execute SELECT DISTINCT query?

Posted by mysqllearner on Stack Overflow See other posts from Stack Overflow or by mysqllearner
Published on 2010-03-23T09:20:31Z Indexed on 2010/03/23 9:23 UTC
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mysql

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distinct

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combine

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tables

I want to calculate how many unique logins from 2 (or probably more tables).

I tried this:

SELECT count(distinct(l1.user_id)) 
FROM `log_1` l1 
LEFT JOIN `log_2` l2 
ON l1.userid = l2.userid;

But it gives me result of l1. If I didnt put l1 on li.userid (distinct), it said "ambiguous".

How do I combine the table, and then select unique login of the combined table?

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