Usage of DISTINCT in mysql

The DISTINCT keyword is used to remove duplicate rows from MySQL query results, leaving only unique values. Its usage includes: DISTINCT column_name: Remove duplicate values from the specified column. DISTINCT(column_name1, column_name2, ...): Remove duplicate values from a combination of multiple columns.

Usage of DISTINCT in MySQL

Question: What is the role of DISTINCT in MySQL?

Answer:
The DISTINCT keyword is used to remove duplicate rows from query results, retaining only unique values.

Detailed description:

DISTINCT has the following usage:

• DISTINCT column_name:Remove duplicates from the specified column value.
• DISTINCT(column_name1, column_name2, ...):Remove duplicate values from a combination of multiple columns.

Note:

• DISTINCT is used to select unique rows, not to filter duplicate values. Duplicate values still exist in the result set, but are not displayed.
• DISTINCT is sensitive to NULL values. NULL values are treated as unique values.
• When using DISTINCT, the ORDER BY clause will affect the order of the results.
• DISTINCT can be used in conjunction with other aggregate functions such as SUM, COUNT, AVG.
• In some cases, using DISTINCT can reduce query performance, especially for large data sets.

Example:

SELECT DISTINCT name FROM customers;

This query will select all unique names from the "customers" table.

SELECT DISTINCT city, country FROM customers;

This query will select unique city and country combinations from the "customers" table.

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