SQL stands for Structured Query Language. It is used to store, manipulate, and retrieve data present in a database server. We use the DISTINCT keyword in SQL with a SELECT statement to remove the duplicate records and return unique records. In this article, we will explore and understand the DISTINCT keyword.
DISTINCT keyword in SQL is a powerful tool for keeping your data tidy and focused. Want to avoid seeing the same record twice?
DISTINCT is your answer.
The Power of Uniqueness:
- Removes Duplicates: When used with the
DISTINCTfilters out duplicate rows based on the specified columns. Imagine a customer table with multiple entries for the same person. Using
customer_namecolumn ensures you only see unique customers.
- Counts Uniques: The
COUNTfunction combined with
DISTINCTreturns the count of unique values in a column. Need to know how many different countries your customers come from? Use
- Multiple Columns: You can specify multiple columns in the
DISTINCTclause. This ensures only rows with unique combinations of those columns appear. Find all cities with distinct combinations of
But It's Not Magic:
- Performance Impact: Removing duplicates requires comparing rows, which can be resource-intensive, especially on large datasets. Use
DISTINCTjudiciously, considering alternative methods like grouping and aggregation when possible.
- Hidden Details:
DISTINCTby default considers all columns in the
SELECTclause for uniqueness. Be mindful of unintended consequences, especially with functions or expressions in your selections.
- Not for Sorting:
DISTINCTdoesn't guarantee any specific order in the results. If order matters, use
Beyond the Basics:
- Using Subqueries: Sometimes, you might need
DISTINCTwithin a subquery to ensure unique results before joining or manipulating data.
- Combining with Aggregation:
DISTINCTcan be used with aggregate functions like
AVGto get unique summaries based on specific criteria.
DISTINCTwhen you absolutely need unique data.
- Consider performance implications, especially on large datasets.
- Understand how multiple columns and functions interact with
- Explore alternative methods like grouping and aggregation when suitable.
With these insights, you can harness the power of
DISTINCT to keep your SQL queries clean, efficient, and focused on the unique information you need.