To get the first record in each group in MySQL, use window functions in MySQL 8.0 or a self join in older versions. 1. In MySQL 8.0 , use ROW_NUMBER() OVER (PARTITION BY group_column ORDER BY sort_column) in a subquery and filter for rn = 1. 2. In pre-8.0 versions, perform a self join by selecting the minimum sort value per group and join back to retrieve full rows. 3. Optimize performance by indexing grouping and sorting columns, avoiding SELECT *, filtering early, or pre-calculating results for large datasets.
When you need to get the first record in each group in MySQL, it’s not as straightforward as some other operations. There's no built-in FIRST() function like there is for MIN() or MAX(), but with a bit of clever query writing, you can achieve exactly what you're after.
Use Case: Why You'd Want the First Record
Before diving into how, let’s quickly cover why someone would want the first record per group. Imagine you have a table tracking user activity and you want to find out what each user did first — like their initial login, first purchase, or earliest interaction. This kind of analysis helps understand user behavior patterns.
1. Using Subqueries and Row Numbers (MySQL 8.0 )
If you're using MySQL 8.0 or newer, the simplest way is by leveraging window functions like ROW_NUMBER().
Here’s how:
SELECT *
FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY group_column ORDER BY sort_column) AS rn
FROM your_table
) AS t
WHERE rn = 1;- Replace
group_columnwith the column that defines your groups (likeuser_id) - Replace
sort_columnwith the column you use to determine what "first" means (likecreated_at)
This method assigns a row number within each group based on your sorting criteria, and then filters only those with row number 1.
? Tip: If you don't care about all columns, just select the ones you need — this can help performance.
2. For Older Versions (Pre-8.0): Self Join Technique
In older versions of MySQL that don’t support window functions, you can simulate this with a self join.
The idea is:
- Find the minimum (or maximum) value per group
- Join back to the original table to get full row details
Example:
SELECT t1.*
FROM your_table t1
JOIN (
SELECT group_column, MIN(sort_column) AS min_val
FROM your_table
GROUP BY group_column
) AS t2
ON t1.group_column = t2.group_column AND t1.sort_column = t2.min_val;This works well if you have an index on group_column and sort_column.
?? Note: If there are ties (i.e., multiple rows with the same min value), this will return all of them. If you want strictly one result, you’ll need additional filtering logic.
3. Performance Considerations
Getting the first record per group can be slow on large datasets if not optimized properly. Here are a few tips:
- Always make sure there’s an index on the grouping and sorting columns
- Avoid using
SELECT *unless necessary - Filter early with WHERE clauses before doing joins or subqueries
For very large tables, sometimes it's better to pre-calculate and store the first record in a separate table or materialized view.
That’s basically it. Depending on your version and data structure, you can choose the method that fits best. It’s not complicated, but it does require knowing a couple of tricks.
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