Introduction to SQL DISTINCT
The DISTINCT keyword in SQL is used to return unique values from a column or set of columns. This can be useful for getting a count of unique values, or for filtering out duplicate rows from a result set.
For example, let’s say we have a table of students, and we want to get a count of the number of unique students in the table. We can use the following SQL query:
SELECT COUNT(DISTINCT student_id)
FROM students;
This query will return the number 10, which is the number of unique students in the student’s table.
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Examples in SQL DISTINCT
Here are some other examples of how to use the DISTINCT keyword in SQL:
- To get a list of all of the unique cities in a country, we could use the following query:
SELECT DISTINCT city
FROM countries;
- To filter out duplicate rows from a list of products, we could use the following query:
SELECT DISTINCT product_name, product_price
FROM products;
Conclusion
The DISTINCT keyword is a powerful tool that can be used to get unique values from a column or set of columns in a SQL database. By understanding how to use the DISTINCT keyword, you can write more efficient and effective SQL queries.