How to Efficiently Find Users with All Three Specified Role IDs?

Select values ​​across rows that meet unique conditions

This question describes a scenario where we have a table with two columns: userid and roleid. The goal is to retrieve a unique userid that has all three specified roleids.

One way is to combine aggregation and filtering:

<code class="language-sql">SELECT userid
FROM userrole
WHERE roleid IN (1, 2, 3)
GROUP BY userid
HAVING COUNT(1) = 3</code>

This query groups the results by userid, counting the occurrences of each roleid for each userid. The HAVING clause ensures that only userids with three different roleids are selected.

However, another approach using joins may be more efficient, especially when working with large data sets:

<code class="language-sql">SELECT t1.userid
FROM userrole t1
JOIN userrole t2 ON t1.userid = t2.userid AND t2.roleid = 2
JOIN userrole t3 ON t2.userid = t3.userid AND t3.roleid = 3
AND t1.roleid = 1</code>

This query utilizes nested joins to select userids based on the specified roleid. The outer join condition checks for the presence of each roleid for each userid, and the final AND condition ensures that the selected userid has all three specified roleids.

Depending on the data distribution and performance characteristics of the underlying database system, either approach may be more appropriate. It is recommended to test both methods to determine the best solution for your specific scenario.

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