Purposes and Functionalities
SELECT DISTINCT:
- Removes duplicate rows: It eliminates rows where all the selected columns have identical values.
- No aggregation: Cannot be used with aggregate functions like SUM, AVG, etc.
- Simpler syntax: Easier to write and understand for basic non-duplication.
- Performance: Can be faster than GROUP BY if no indexes are used, as it avoids sorting.
GROUP BY:
- Grouping data: Creates groups of rows based on shared values in one or more columns.
- Aggregation: Used with aggregate functions to summarize data within each group (e.g., COUNT, MAX, AVG).
- More complex: Requires specifying group columns and aggregate functions.
- Sorting: Generally involves sorting data, which can impact performance.
Choosing between them
- Use SELECT DISTINCT when you simply want to eliminate duplicate rows without summarizing data.
- Use GROUP BY when you need to group data and perform aggregations within each group.
|
Feature |
SELECT DISTINCT |
GROUP BY |
|---|---|---|
|
Purpose |
Remove duplicate rows |
Group data and aggregate |
|
Aggregate functions |
No |
Yes |
|
Sorting |
No (optional) |
Yes (default) |
|
Performance |
Can be faster (no index) |
Slower (sorting) |
|
Syntax |
Simpler |
More Complex |
SELECT DISTINCT vs GROUP BY in MySQL
In MySQL, the two most common ways of managing and retrieving unique values are with SELECT and GROUP BY. However, they are used for different reasons. With SELECT, we can get different values from the same column, so we don’t have to worry about duplicates. With GROUP BY, we can aggregate data and group results based on specific columns. However, there are some differences between the two operators. Both can be used to generate the same output. But we need to know the difference for better utilization of resources and time.
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