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SQLite Select Distinct

Summary: in this tutorial, you will learn how to use the SQLite SELECT DISTINCT clause to remove duplicate rows in the result set.

Introduction to SQLite SELECT DISTINCT clause

The DISTINCT clause is an optional clause of the  SELECT statement. The DISTINCT clause allows you to remove the duplicate rows in the result set.

The following statement illustrates the syntax of the DISTINCT clause:

SELECT DISTINCT	select_list
FROM table;Code language: SQL (Structured Query Language) (sql)

In this syntax:

  • First, the DISTINCT clause must appear immediately after the SELECT keyword.
  • Second, you place a column or a list of columns after the DISTINCT keyword. If you use one column, SQLite uses values in that column to evaluate the duplicate. In case you use multiple columns, SQLite uses the combination of values in these columns to evaluate the duplicate.

SQLite considers NULL values as duplicates. If you use theDISTINCT clause with a column that has NULL values, SQLite will keep one row of a NULL value.

In database theory, if a column contains NULL values, it means that we do not have the information about that column of particular records or the information is not applicable.

For example, if a customer has a phone number with a NULL value, it means we don’t have information about the phone number of the customer at the time of recording customer information or the customer may not have a phone number at all.

SQLite SELECT DISTINCT examples

We will use the customers table in the sample database for demonstration.