How to Retrieve the Highest Version Record for Each ID in MySQL\'s GROUP BY Clause?

Controlling the Returned Row in MySQL Group By

In MySQL, retrieving the desired row from a group of data can pose a challenge. This article explores how to establish control over the returned row in a group by scenario.

Problem:

A database table contains multiple versions of records identified by an id column and a version_id column. The goal is to query the table and return only the record with the highest version_id for each unique id.

Solution 1 (Subquery Approach):

One approach involves using a subquery to rank the rows based on the version_id in descending order:

SELECT *
FROM (SELECT * FROM table ORDER BY version_id DESC) t1
GROUP BY t1.id

This method effectively creates a temporary table, sorts the data, and then groups it to retrieve the desired row.

Solution 2 (Using Max and Joins):

Another method utilizes the MAX() function and joins to achieve the same result:

SELECT *
FROM (SELECT id, MAX(version_id) AS version_id FROM table GROUP BY id) t1
INNER JOIN table t2 ON t2.id = t1.id AND t1.version_id = t2.version_id

This approach first identifies the maximum version_id for each id and then joins the original table to obtain the complete record with the highest version.

Advantages and Considerations:

The subquery approach can create a temporary table in memory, which may impact performance for large datasets. On the other hand, it can be simpler to understand and implement.

The join-based method is generally more efficient for larger datasets as it avoids creating a temporary table. However, it assumes the presence of an index on the (id, version_id) columns for optimal performance.

Both solutions require a suitable index for efficient execution.

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