What does DISTINCT mean in mysql?

DISTINCT is an operator used in MySQL to remove duplicate rows from a result set. It retains unique values within the same column or set of columns. Usage: 1. Used with the SELECT statement to select unique values from a table. 2. Syntax: SELECT DISTINCT column_name(s) FROM table_name. 3. For example: SELECT DISTINCT name FROM customers;

What is DISTINCT in MySQL?

DISTINCT is an operator in MySQL that is used to remove duplicate rows from the result set. It only keeps unique values in the same column or set of columns.

Usage of DISTINCT

DISTINCT is typically used with the SELECT statement to select unique values from a table. The syntax is as follows:

SELECT DISTINCT column_name(s) FROM table_name;

Where:

• column_name(s)is the column name to filter out unique values.
• table_nameis the name of the table to be queried.

For example, to select the names of unique customers from thecustomerstable, you can use the following query:

SELECT DISTINCT name FROM customers;

How to understand DISTINCT

The DISTINCT operator works by comparing the values of each row in the returned result set. If two rows have the same comparison value, one of the rows will be discarded and only the unique row will be retained.

Differences from DISTINCTROW

DISTINCT is similar to the DISTINCTROW operator, but there are some key differences between the two:

• DISTINCT only Removes duplicate rows based on specified columns, while DISTINCTROW removes all duplicate rows.
• DISTINCTROW is generally less efficient than DISTINCT.

Best Practices for Using DISTINCT

• Use DISTINCT on columns where you want to filter out unique elements.
• Use DISTINCT when you need to eliminate duplicate values in an aggregate function.
• Avoid using DISTINCT on large data sets as it may significantly reduce performance.

The above is the detailed content of What does DISTINCT mean in mysql?. For more information, please follow other related articles on the PHP Chinese website!